Best answer by Adzdalton
So after a little looking around i think i've found something you could try.
-Turn off iMessage in settings > Messages and restart your phone
-Go back to settings, phone and then My number.
(Check to see if this displays your number, if not enter your number)
-Then turn iMessage back on in the settings
-Go back to settings > Messages > Send & Recieve and check to see if the correct number is displayed under the "Start new conversations: from"
This seems to happen after porting a number across.
Hope this helps :)