let me quote from another forum, because I don´t know the solution
I'll jump in and suggest you do exactly as jbdan suggests - listen to the voice menu when you dial *228, and select option 1.
Set your phone down (perhaps you can listen to it on speakerphone) while it is doing it's thing, and leave it alone until the (automated) voice on the phone indicates that programming is complete.
Then try a text message (send one to yourself for the quickest test!) and report back if this fixes your problem.