sms.class = 0  invalid syntax

Hi

I tried the example, but it doesn't work, it says "invalid syntax"
Of course on my pc I used my phone number

```
from messaging.sms import SmsSubmit

sms = SmsSubmit("+44123231231", "hey how's it going?")
sms.class = 0
pdu = sms.to_pdu()[0]

print pdu.length, pdu.pdu
```

result:
  File "send_sms.py", line 6
    sms.class = 0
            ^
SyntaxError: invalid syntax
