The result i found was to do with area info. Go to messages and select settings. make sure you go into area info and select reception ON. This corrected my problem i had with not sending messages.

This could be as a result of very poor network in your location.

Check your signal bar to verify if the network strenght or signal is ok.

Secondly you may have not properly configured your SMS settings in your phone.

Go to messages and select settings. make sure your network service message centre number is selected or active or enabled. If you dont know what to do select the default message centre number.

If this problem persist call your customer care for further support