Same problem here and after I read through all comments it can certainly not be an issue of the network operator(s). Since, everyone uses different operators and the issues occurs in many different countries and occured for the first time already in 2012. (You would expect it is solved by now!)
I have my iPhone 5s only 1 week and the problem has occured now. The hint with resetting the network settings has worked for me (at least for the moment...). However, this is still not a solution for the problem in general. I miss customer support and an initiative from Apple here!!!
on 8/13 my iphone 5s died from not being charged when I was able to get it charged it had "no service" at the top. when I do get any signal it is 1 bar and says extended. I have been through all the troubleshooting with verizon including a new sim card. Apple insist its a network problem but verizon can not resolve the issue. I would appreciate any help
I have had this problem for a year and thought I'd tried everything but I believe I've now fixed it. I turned off automatic carrier selection (Settings/Carriers/Automatic) and waited an age before it came up with the available operators (EE, Vodaphone, 3, O2). I selected EE and since then it hasn't once shown no service.
I hope this helps others.
Using old phone with service still on you call 611 and follow the prompts. Had to power off the new one and It took 5 minutes for ATT to activate the new one, the old one changed to emergency calls only. However on my new iPhone 6s Plus I am greeted with one bar of signal on ATT. Wow do I want to cancel my att service, send the phone back, and jump to another carrier. I also feel like I've gone two years backwards to this latest 6s plus from my Sony Expedia z3 with 4K video and superior music. Looking for the z5 release dates now.
I was having the same problem as of yesterday and did a google search to find this forum. My problem was that I was a victim of fraud. Someone in FL (not my home state) walked into an Apple store and upgraded my phone and my service was shutoff. Not sure how this could happen since it seems like I have to provide all sorts of information to prove my identity (at least with ATT) however, it appears Apple stores do not have the same policy or some obviously do not. .