Hi. I have an iPhone 4, running iOS 5.1.1, firmware 4.12.02. I have service with 3 UK, have had for a year and it's been fine. My husband has the same phone, same service provider, yet for some reason when we go abroad (to the US), his phone connects to AT&T, and mine doesn't. Never really cared, but it might be relevant to my problem. Last night, I noticed that my phone was showing No Service, so I switched it into Airplane Mode and off again. Straight back to No Service. So I turned the phone off, and then on again. Searched for a sec, then back to No Service. Normally, in my flat I have full bars, and while I had this No Service, my husband still had full bars. So we check to make sure the bill is paid up; it is. Then, we swap micro sim cards: mine works in his phone, his shows No Service in mine. So that means it's not the sim, and it must be the phone right? Hmm. I try all the standard things, but when I go to Settings > General > Network, I get the message "Phone Not Allowed". When I go to Settings > Carrier > Turn Automatic Carriers "Off", and select the 3 network, I get a message saying "Your selected cellular network is restricted." I try resetting Network Settings- nothing. I decide that maybe now is the time to update iOS to 6.0.1. I back up my phone data, and I update, still No Service! So I restore to factory settings (which obviously keeps the iOS at 6.0.1)- No Service. At this point, I am at a loss as to what to do. I don't really want to mess with it more, and I'm not finding helpful answers elsewhere on the internet, so we just leave it. This morning, still No Service. My husband was leaving to go abroad for work, and it was more important for me to have a working phone, so we swapped sim cards again, and he took the No Service phone with him, with his sim in it. He's texted me from the US, and has successfully connected to the AT&T network there! What is going on? I've got 5 days left on my return policy from the store where I bought the phone, so I need to know if this is a problem with 3 or the phone. I tried calling 3, but I'm not the account holder and husband is abroad so I couldn't do anything. Do I take it to Apple or 3? And if it works itself out before then, should I exchange it anyway, in case this happens again, and by then it will be too late to exchange the phone? Sorry for the really long post, but I wanted to be thorough. Any help is greatly appreciated.