Ensure that the SMS Message Centre Number or Service Centre Number in your handset is updated. The message centre ensures that your text message is sent to the recipient. If the message centre number in your phone is blank, the text message can't be sent. This is normally updated under SMS Settings in your handset.
For Android devices in general:
Launch the SMS application on your phone
Tap on Menu and go to Settings
Scroll down and select 'Message Centre' (If you cannot find Message centre in this list then look for and tap Text message and it should hopefully be in this list)
As soon as you open that, you'll be able to see and edit the message centre number
If blank, enter in the number 1234 and click on OK.
Restart your phone and send ‘test’ text to check if its working
If your Android phone doesn't have the 'Message Centre' option available, then you can find the same by:
Typing *#*#4636#*#* into your phone on the dial screen
Select Phone information
Scroll down and select the SMSC setting
Press Refresh to see the current setting
If the number is blank then type 1234 and press Update
Restart your phone and send test text to make sure it’s working