I've had my phone for about 7 months. I've had no problems with it until now. I was using the internet on the phone with a 3G connection. After awhile, the internet pages wouldn't load up and I noticed the 3G symbol had changed into a larger G. I still had signal bars but no connection. After a few minutes waiting for it to reconnect, I decided to just power off the phone and restart it.
When the phone booted up I got several signal bars but (NO SERVICE) appeared on the screen. When I tried to make a call it says, "No Registered On Network". After talking to AT&T customer service, they thought it was my sim card. So, I bought another one and still the same thing. Then they thought it might be the signal reception in my area. That was ruled out and I can make calls with other AT&T phones.
I've done a factory reset and still nothing. Any ideas? Is there a setting that could have been changed that would prevent my from registering on the network? I'm out of ideas.