I had a iphone 4s and the lock button stopped working so two weeks ago I got a new one. When I got it everything was working perfectly fine. Now when I try and text some of my contacts I keep getting this "not delivered !" message. If even pops up when I had full service. Also people say that when they try to text me it will not send and when they try and call me they get some voice message. I would like to know what can be done to fix this problem because I have tried everything ?