Common issue for iPhones after the phone number change is it's still showing the old phone number. If this happens, follow these procedures:
1.) Go to Settings.
2.) Go to Phone then tap on the mobile number field then change the number to the new mobile number.
3.) Turn off the phone and turn it back on.
4.) Send text to your own number to check if it’ll show the old number.
IF the old phone number still shows, follow these steps:
1.) Switched off Face Time (Setting > FaceTime > FaceTime OFF)
2.) Switched off iMessage(Setting > Messages >iMessage OFF)
3.)Switched on iMessage (The phone will show “Verifying"). If it failed set it to the correct phone number (Settings > Messages > Receive At > Phone).
4.) At this point the “My Number” (Settings >Phone > My Number) had also updated.
5.) Switched on FaceTime(Same as with iMessage will show "Verifying", but take two attempts).
6.) Power Cycle/reboot the phone and re-synced to updateiTunes (Summary “Phone Number” field).
**Note: Some procedures may not be available on iPhone 4S.