You could have a SIM issue. Try pulling it out and reseating it.
Contact your carrier.
Solution; there isn't one. iPhone 5 is flawed as a phone. After getting two replacements with the same issue, and having Apple service team refusing to talk to me, I've found a solution by myself.
I'm getting a nexus 4 and I'm waiting for the press to have a field day with "antennagate 2"!!
You're trolling several threads. Do you feel better?
Mine does that from time to time. Since the carrier made a major screwup this Xmas by selling too many of the gadgets and thereby crashing their LTE network and are now feverishly trying to repair the damage setting up new celltowers all over, I blame it on their halfassed efforts.
But back to the problem. Sometimes it corrects itself unaided. Sometimes, switching on Airplane Mode (all radios off) and off causes it to relink as it does a new carrier search. Else, I have to resort to turning it off altogether and back on again; you know, hold down the top button for awhile till the red swipe bar pops up. I have my Settings / Carrier set to Auto, but the SIM will ensure it remains locked to the right one, if this helps any.
A little while ago I was researching if it could operate without a SIM card and caught it in the middle of a No Service brainfart. Taking the SIM out and putting it back in did restore service, but since it was off for both the out and the in, this counts as Option #3 from above. Do NOT think the SIM is hot-pluggable and will NOT research that option.
Oh, and yeah, works just fine without the SIM, after it b.i.t.c.h.e.s and moans about it missing. Thinks its an iPod Touch on steroids.
I apologise for being negative. once I would have jumped to defend Apple too, but those days are over.
I have spent £600 on a product that I am going to have to sell at a loss of £300, having spent many previous hours trying to get it to work, plus a 70 mile round trip to my nearest apple store. I estimate the lost income and depreciation overall to have cost in excess of £600.
I have tried 4 sim cards on two networks (having moved from the phone network that I'd been on for 20 years in a desperate attempt to find a solution) in 3 iphone 5's, all with the same problem
And the final insult is that Apple no longer bothers to assit me; they don't return my calls or emails; nothing
I love everything else about the phone, so I've just installed the new software version and hope that will fix it. Otherwise my Nexus 4 arrived in the post today, so I will start using that if I get the problem again
I used to love Apple but they have let me down.
My reason for posting on these forums was to warn people that it is not your phone, it is EVERY iphone 5 that has the problem. Therefore don't waste your time getting a replacement.
Sorry for being negative, but that is how I feel!