diff --git a/src/Client.php b/src/Client.php
index 77036f4..e8140c9 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -18,26 +18,24 @@
  */
 class Client extends ResourceCollection
 {
-    const BASE_URL = 'https://rest.nexmo.com/';
-
-    /**
-     * @var string
-     */
-    private $apiKey;
-
     /**
-     * @var string
+     * @var array
      */
-    private $apiSecret;
+    private $options = array(
+        'apiKey' => null,
+        'apiSecret' => null,
+        'baseURL' => 'https://rest.nexmo.com/',
+        'debug' => false,
+        'timeout' => 5.0,
+    );
 
     /**
-     * @param string $apiKey
-     * @param string $apiSecret
+     * @param array $options
      */
-    public function __construct($apiKey, $apiSecret)
+    public function __construct(Array $options = [])
     {
-        $this->apiKey = $apiKey;
-        $this->apiSecret = $apiSecret;
+        // Override default options with options provided during instantiation.
+        $this->options = array_merge($this->options, $options);
     }
 
     protected function getNamespace()
@@ -57,11 +55,13 @@ protected function loadClient()
             return;
         }
         $this->client = new HttpClient([
-            'base_url' => static::BASE_URL,
+            'base_url' => $this->options['baseURL'],
             'defaults' => [
+                'timeout' => $this->options['timeout'],
+                'debug' => $this->options['debug'],
                 'query' => [
-                    'api_key' => $this->apiKey,
-                    'api_secret' => $this->apiSecret
+                    'api_key' => $this->options['apiKey'],
+                    'api_secret' => $this->options['apiSecret']
                 ]
             ]
         ]);
diff --git a/src/RateLimitSubscriber.php b/src/RateLimitSubscriber.php
new file mode 100644
index 0000000..20cd9c1
--- /dev/null
+++ b/src/RateLimitSubscriber.php
@@ -0,0 +1,81 @@
+<?php
+namespace Nexmo;
+use GuzzleHttp\Event\BeforeEvent;
+use GuzzleHttp\Event\CompleteEvent;
+use GuzzleHttp\Event\SubscriberInterface;
+
+class RateLimitSubscriber implements SubscriberInterface
+{
+    /**
+     * @param array $time
+     * Rate limit for the SMS and Voice API is on a per-LVN/shortcode basis, so we record durations in an array with the LVN as the key.
+     * For maximum throughput messages should be sent from different LVNs in an interleaved patter, e.g., 1, 2, 3, 1, 2, 3 instead of 1, 1, 2, 2, 3, 3
+     * (or better, send from each LVN in parallel, concurrent threads).
+     */
+    private static $time = [];
+
+    /**
+     * @param float $max_requests_per_sec
+     * Max number of requests per second. Nexmo's most restrictive API is the SMS API for US/Canada -> US/Canada routing at 1/sec, let's be safe and use that as default.
+     */
+    private $maxRequestsPerSec = 1;
+
+    /**
+     * @param string $timeKey
+     * LVN/shortcode when using the SMS or Voice API. Left as a blank string for the Developer API.
+     */
+    private $timeKey = '';
+
+    /**
+     * @param int $rate
+     */
+    public function setRate($rate)
+    {
+        $this->maxRequestsPerSec = $rate;
+    }
+
+    /**
+     * @param string $key
+     */
+    public function setKey($key)
+    {
+        $this->timeKey = $key;
+    }
+
+    /**
+     * @return array
+     */
+    public function getEvents()
+    {
+        return [
+            'before'   => ['onBefore'],
+            'complete' => ['onComplete'],
+        ];
+    }
+
+    /**
+     * @param BeforeEvent $event
+     */
+    public function onBefore(BeforeEvent $event)
+    {
+        self::$time[$this->timeKey] = microtime(true);
+    }
+
+    /**
+     * @param CompleteEvent $event
+     */
+    public function onComplete(CompleteEvent $event)
+    {
+        // Convert requests-per-second to a minimum duration in seconds.
+        $min_request_duration_sec = 1 / $this->maxRequestsPerSec;
+
+        // Calculate the duration of the previous request in seconds.
+        $elapsed_sec = microtime(true) - self::$time[$this->timeKey];
+
+        // If the duration is greater than the minimum duration, for this LVN, we must delay.
+        if ($elapsed_sec < $min_request_duration_sec) {
+            $min_request_duration_microsec = ($min_request_duration_sec - $elapsed_sec) * 1000000;
+            usleep($min_request_duration_microsec);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/Service/Account/Balance.php b/src/Service/Account/Balance.php
index 5156e03..f20b039 100644
--- a/src/Service/Account/Balance.php
+++ b/src/Service/Account/Balance.php
@@ -12,6 +12,15 @@
  */
 class Balance extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
     /**
      * @inheritdoc
      */
diff --git a/src/Service/Account/Numbers.php b/src/Service/Account/Numbers.php
index 8a86bc9..ee3214f 100644
--- a/src/Service/Account/Numbers.php
+++ b/src/Service/Account/Numbers.php
@@ -14,6 +14,15 @@
  */
 class Numbers extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
     /**
      * @inheritdoc
      */
@@ -51,6 +60,10 @@ protected function validateResponse(array $json)
         if (!isset($json['count'])) {
             throw new Exception('count property expected');
         }
+        if (0 == $json['count']) {
+            // If there are no numbers on the account, stop validating.
+            return;
+        }
         if (!isset($json['numbers']) || !is_array($json['numbers'])) {
             throw new Exception('numbers array property expected');
         }
@@ -67,9 +80,6 @@ protected function validateResponse(array $json)
             if (!isset($number['features']) || !is_array($number['features'])) {
                 throw new Exception('number.features array property expected');
             }
-            if (!isset($number['moHttpUrl'])) {
-                throw new Exception('number.moHttpUrl property expected');
-            }
         }
     }
 }
diff --git a/src/Service/Account/Pricing/Country.php b/src/Service/Account/Pricing/Country.php
index d88ebb1..77bdf65 100644
--- a/src/Service/Account/Pricing/Country.php
+++ b/src/Service/Account/Pricing/Country.php
@@ -13,6 +13,15 @@
  */
 class Country extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API permits 3/sec max.
+        return 2;
+    }
+
     /**
      * @inheritdoc
      */
@@ -34,7 +43,8 @@ public function invoke($country = null)
         }
 
         return new Entity\Pricing($this->exec([
-            'country' => $country,
+            // Nexmo API requires $country value to be uppercase.
+            'country' => strtoupper($country),
         ]));
     }
 
@@ -43,6 +53,10 @@ public function invoke($country = null)
      */
     protected function validateResponse(array $json)
     {
+        if (!isset($json['mt'])) {
+            // Some countries don't have any values, e.g., BV.
+            return;
+        }
         if (!isset($json['country'])) {
             throw new Exception('country property expected');
         }
diff --git a/src/Service/Account/Pricing/International.php b/src/Service/Account/Pricing/International.php
index dac7716..faea2ed 100644
--- a/src/Service/Account/Pricing/International.php
+++ b/src/Service/Account/Pricing/International.php
@@ -12,6 +12,15 @@
  */
 class International extends Country
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
     /**
      * @inheritdoc
      */
diff --git a/src/Service/Account/Pricing/Phone.php b/src/Service/Account/Pricing/Phone.php
index 9137d1d..88148ad 100644
--- a/src/Service/Account/Pricing/Phone.php
+++ b/src/Service/Account/Pricing/Phone.php
@@ -13,6 +13,15 @@
  */
 class Phone extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
     /**
      * @var string
      */
diff --git a/src/Service/Message.php b/src/Service/Message.php
index c724c15..49da864 100644
--- a/src/Service/Message.php
+++ b/src/Service/Message.php
@@ -11,6 +11,20 @@
  */
 class Message extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit($params = null)
+    {
+        if (preg_match('/^1\d{10}$/', $params['from']) && preg_match('/^1\d{10}$/', $params['to'])) {
+            // SMS from US/Canadian LVN to US/Canadian recipient has a 1/sec rate limit.
+            // https://help.nexmo.com/hc/en-us/articles/203993598
+            return 1;
+        }
+        // For all others, Nexmo Voice API has a 30/sec rate limit.
+        return 30;
+    }
+
     /**
      * @return string
      */
@@ -83,7 +97,8 @@ public function invoke(
             throw new Exception("\$text parameter cannot be blank");
         }
 
-        if ($type === 'text' && $this->containsUnicode($text)) {
+        // If $type is empty, 'text' will be assumed by Nexmo's SMS API.
+        if (($type == '' || $type === 'text') && $this->containsUnicode($text)) {
             $type = 'unicode';
         }
 
@@ -104,9 +119,38 @@ public function invoke(
         ]);
     }
 
+    /**
+     * @param string $text
+     * @return int
+     */
     protected function containsUnicode($text)
     {
-        return max(array_map('ord', str_split($text))) > 127;
+        // Valid GSM default character-set codepoint values from http://unicode.org/Public/MAPPINGS/ETSI/GSM0338.TXT
+        $gsm_0338_codepoints = [0x0040, 0x00A3, 0x0024, 0x00A5, 0x00E8, 0x00E9, 0x00F9, 0x00EC, 0x00F2, 0x00E7, 0x000A, 0x00D8, 0x00F8, 0x000D, 0x00C5, 0x00E5, 0x0394, 0x005F, 0x03A6, 0x0393, 0x039B, 0x03A9, 0x03A0, 0x03A8, 0x03A3, 0x0398, 0x039E, 0x00A0, 0x000C, 0x005E, 0x007B, 0x007D, 0x005C, 0x005B, 0x007E, 0x005D, 0x007C, 0x20AC, 0x00C6, 0x00E6, 0x00DF, 0x00C9, 0x0020, 0x0021, 0x0022, 0x0023, 0x00A4, 0x0025, 0x0026, 0x0027, 0x0028, 0x0029, 0x002A, 0x002B, 0x002C, 0x002D, 0x002E, 0x002F, 0x0030, 0x0031, 0x0032, 0x0033, 0x0034, 0x0035, 0x0036, 0x0037, 0x0038, 0x0039, 0x003A, 0x003B, 0x003C, 0x003D, 0x003E, 0x003F, 0x00A1, 0x0041, 0x0042, 0x0043, 0x0044, 0x0045, 0x0046, 0x0047, 0x0048, 0x0049, 0x004A, 0x004B, 0x004C, 0x004D, 0x004E, 0x004F, 0x0050, 0x0051, 0x0052, 0x0053, 0x0054, 0x0055, 0x0056, 0x0057, 0x0058, 0x0059, 0x005A, 0x00C4, 0x00D6, 0x00D1, 0x00DC, 0x00A7, 0x00BF, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, 0x0068, 0x0069, 0x006A, 0x006B, 0x006C, 0x006D, 0x006E, 0x006F, 0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x0077, 0x0078, 0x0079, 0x007A, 0x00E4, 0x00F6, 0x00F1, 0x00FC, 0x00E0];
+
+        // Split $text into an array in a way that respects multibyte characters.
+        $text_chars = preg_split('//u', $text, null, PREG_SPLIT_NO_EMPTY);
+
+        // Array of codepoint values for characters in $text.
+        $text_codepoints = array_map([$this, 'uord'], $text_chars);
+
+        // Filter the array to contain only codepoints from $text that are not in the set of valid GSM codepoints.
+        $non_gsm_codepoints = array_diff($text_codepoints, $gsm_0338_codepoints);
+
+        // The text contains unicode if the result is not empty.
+        return !empty($non_gsm_codepoints);
+    }
+
+    /**
+     * @param char $unicode_char
+     * @return int
+     */
+    public function uord($unicode_char)
+    {
+        $k = mb_convert_encoding($unicode_char, 'UCS-2LE', 'UTF-8');
+        $k1 = ord(substr($k, 0, 1));
+        $k2 = ord(substr($k, 1, 1));
+        return $k2 * 256 + $k1;
     }
 
     /**
diff --git a/src/Service/Number.php b/src/Service/Number.php
new file mode 100644
index 0000000..2912972
--- /dev/null
+++ b/src/Service/Number.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Nexmo\Service;
+
+use Nexmo\Entity;
+use Nexmo\Entity\MatchingStrategy;
+use Nexmo\Exception;
+
+/**
+ * Class Number
+ * @package Nexmo\Service
+ */
+class Number extends ResourceCollection
+{
+    /**
+     * @return array
+     * @throws Exception
+     */
+    public function search($country = null, $index = 1, $size = 10, $pattern = null, $searchPattern = MatchingStrategy::STARTS_WITH, $features = 'SMS')
+    {
+        return $this->search->invoke($country, $index, $size, $pattern, $searchPattern, $features);
+    }
+
+    /**
+     * @return array
+     * @throws Exception
+     */
+    public function buy($country, $msisdn)
+    {
+        return $this->buy->invoke($country, $msisdn);
+    }
+    /**
+     * @return array
+     * @throws Exception
+     */
+    public function cancel($country, $msisdn)
+    {
+        return $this->cancel->invoke($country, $msisdn);
+    }
+}
diff --git a/src/Service/Number/Buy.php b/src/Service/Number/Buy.php
new file mode 100644
index 0000000..ad9b06f
--- /dev/null
+++ b/src/Service/Number/Buy.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace Nexmo\Service\Number;
+
+use Nexmo\Entity\MatchingStrategy;
+use Nexmo\Entity\NumberCollection;
+use Nexmo\Exception;
+use Nexmo\Service\Service;
+
+/**
+ * Get all inbound numbers associated with your account.
+ *
+ * @author Carson Full <carsonfull@gmail.com>
+ */
+class Buy extends Service
+{
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getEndpoint()
+    {
+        return 'number/buy';
+    }
+
+    /**
+     * @param string     $country
+     * @param string     $msisdn
+     *
+     * @return boolean
+     * @throws Exception
+     */
+    public function invoke($country = null, $msisdn = null)
+    {
+        if (!$country) {
+            throw new Exception("\$country parameter cannot be blank");
+        }
+        if (!$msisdn) {
+            throw new Exception("\$msisdn parameter cannot be blank");
+        }
+
+        return $this->exec([
+            // Nexmo API requires $country value to be uppercase.
+            'country' => strtoupper($country),
+            'msisdn' => $msisdn,
+        ], 'POST');
+    }
+
+
+    /**
+     * @inheritdoc
+     */
+    protected function validateResponse(array $json)
+    {
+        if (!isset($json['error-code'])) {
+            throw new Exception('no error code');
+        }
+
+        switch ($json['error-code']) {
+        case '200':
+            return true;
+
+        case '401':
+            throw new Exception('error 401 wrong credentials');
+
+        case '420':
+            throw new Exception('error 420 wrong parameters');
+
+        default:
+            throw new Exception('unknown error code');
+        }
+    }
+}
diff --git a/src/Service/Number/Cancel.php b/src/Service/Number/Cancel.php
new file mode 100644
index 0000000..96c7cb3
--- /dev/null
+++ b/src/Service/Number/Cancel.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace Nexmo\Service\Number;
+
+use Nexmo\Entity\MatchingStrategy;
+use Nexmo\Entity\NumberCollection;
+use Nexmo\Exception;
+use Nexmo\Service\Service;
+
+/**
+ * Get all inbound numbers associated with your account.
+ *
+ * @author Carson Full <carsonfull@gmail.com>
+ */
+class Cancel extends Service
+{
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getEndpoint()
+    {
+        return 'number/cancel';
+    }
+
+    /**
+     * @param string     $country
+     * @param string     $msisdn
+     *
+     * @return boolean
+     * @throws Exception
+     */
+    public function invoke($country = null, $msisdn = null)
+    {
+        if (!$country) {
+            throw new Exception("\$country parameter cannot be blank");
+        }
+        if (!$msisdn) {
+            throw new Exception("\$msisdn parameter cannot be blank");
+        }
+
+        return $this->exec([
+            // Nexmo API requires $country value to be uppercase.
+            'country' => strtoupper($country),
+            'msisdn' => $msisdn,
+        ], 'POST');
+    }
+
+
+    /**
+     * @inheritdoc
+     */
+    protected function validateResponse(array $json)
+    {
+        if (!isset($json['error-code'])) {
+            throw new Exception('no error code');
+        }
+
+        switch ($json['error-code']) {
+        case '200':
+            return true;
+
+        case '401':
+            throw new Exception('error 401 wrong credentials');
+
+        case '420':
+            throw new Exception('error 420 wrong parameters');
+
+        default:
+            throw new Exception('unknown error code');
+        }
+    }
+}
diff --git a/src/Service/Number/Search.php b/src/Service/Number/Search.php
new file mode 100644
index 0000000..4282936
--- /dev/null
+++ b/src/Service/Number/Search.php
@@ -0,0 +1,66 @@
+<?php
+namespace Nexmo\Service\Number;
+
+use Nexmo\Entity\MatchingStrategy;
+use Nexmo\Entity\NumberCollection;
+use Nexmo\Exception;
+use Nexmo\Service\Service;
+
+class Search extends Service
+{
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getEndpoint()
+    {
+        return 'number/search';
+    }
+
+    /**
+     * @param int        $index
+     * @param int        $size
+     * @param string|int $pattern
+     * @param int        $searchPattern
+     *
+     * @return NumberCollection
+     * @throws Exception
+     */
+    public function invoke($country = null, $index = 1, $size = 10, $pattern = null, $searchPattern = MatchingStrategy::STARTS_WITH, $features = 'SMS')
+    {
+        if (!$country) {
+            throw new Exception("\$country parameter cannot be blank");
+        }
+
+        $size = min($size, 100);
+
+        return new NumberCollection($this->exec([
+            // Nexmo API requires $country value to be uppercase.
+            'country' => strtoupper($country),
+            'index' => $index,
+            'size' => $size,
+            'pattern' => $pattern,
+            'search_pattern' => $searchPattern,
+            'features' => $features,
+        ]));
+    }
+
+    /**
+     * @inheritdoc
+     */
+    protected function validateResponse(array $json)
+    {
+        // If the 'numbers' element exists (which it won't if no numbers are available for a search), validate it is an array.
+        if (isset($json['numbers']) && !is_array($json['numbers'])) {
+            throw new Exception('numbers property not an array');
+        }
+    }
+}
diff --git a/src/Service/ResourceCollection.php b/src/Service/ResourceCollection.php
index 82a184e..c59d292 100644
--- a/src/Service/ResourceCollection.php
+++ b/src/Service/ResourceCollection.php
@@ -39,6 +39,7 @@ public function __get($name)
             }
             $cls = $this->initializeClass($clsName);
             $cls->setClient($this->client);
+            $cls->rateLimitSubscriber = new \Nexmo\RateLimitSubscriber();
 
             $this->resources[$name] = $cls;
         }
diff --git a/src/Service/Service.php b/src/Service/Service.php
index a9013b0..4576ccc 100644
--- a/src/Service/Service.php
+++ b/src/Service/Service.php
@@ -11,6 +11,11 @@
  */
 abstract class Service extends Resource
 {
+    /**
+     * @return int
+     */
+    abstract public function getRateLimit();
+
     /**
      * @return string
      */
@@ -32,13 +37,24 @@ abstract protected function validateResponse(array $json);
      * @throws Exception
      * @return array
      */
-    protected function exec($params)
+    protected function exec($params, $method = 'GET')
     {
         $params = array_filter($params);
 
-        $response = $this->client->get($this->getEndpoint(), [
+        // Configure the RateLimitSubscriber for this request.
+        $this->rateLimitSubscriber->setRate($this->getRateLimit($params));
+        $this->rateLimitSubscriber->setKey(isset($params['from']) ? $params['from'] : '');
+
+        // Attach the RateLimitSubscriber with these settings.
+        $this->client->getEmitter()->attach($this->rateLimitSubscriber);
+
+        // Send the request using the specified method, endpoint and query params.
+        $response = $this->client->send($this->client->createRequest($method, $this->getEndpoint(), [
             'query' => $params
-        ]);
+        ]));
+
+        // Must remove the RateLimitSubscriber after each request.
+        $this->client->getEmitter()->detach($this->rateLimitSubscriber);
 
         try {
             $json = $response->json();
@@ -46,7 +62,10 @@ protected function exec($params)
             throw new Exception($e->getMessage(), 0, $e);
         }
 
-        $this->validateResponse($json);
+        // Because validateResponse() expects an array, we can only do so if the response body is not empty (which in some cases is a valid response), otherwise $json will be null.
+        if (strlen($response->getBody()) > 0) {
+            $this->validateResponse($json);
+        }
 
         return $json;
     }
diff --git a/src/Service/Verify.php b/src/Service/Verify.php
index f7eeec1..6307c93 100644
--- a/src/Service/Verify.php
+++ b/src/Service/Verify.php
@@ -11,6 +11,15 @@
  */
 class Verify extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
     /**
      * @var VerifyCheck
      */
diff --git a/src/Service/VerifyCheck.php b/src/Service/VerifyCheck.php
index faf3574..a1d1546 100644
--- a/src/Service/VerifyCheck.php
+++ b/src/Service/VerifyCheck.php
@@ -10,6 +10,15 @@
  */
 class VerifyCheck extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo developer API claims 3/sec max, but actually more than 2/sec causes error 429 Too Many Requests.
+        return 2;
+    }
+
 
     /**
      * @return string
diff --git a/src/Service/Voice.php b/src/Service/Voice.php
index 7839fe2..bbb9215 100644
--- a/src/Service/Voice.php
+++ b/src/Service/Voice.php
@@ -10,6 +10,15 @@
  */
 class Voice extends Service
 {
+    /**
+     * @inheritdoc
+     */
+    public function getRateLimit()
+    {
+        // Max number of requests per second. Nexmo Voice API has a 30/sec rate limit.
+        return 30;
+    }
+
     /**
      * @return string
      */