Connie - Out of curiosity what state are you in? I'm in MN and my daughter is having the same problem. I'm wondering it's it's tied to a certain network/locale.
I had this issue on my 2nd. day. The first day the phone worked fine, the second day it would not recognize the sim card. The only thing that I did in between was to put a case on it. Maybe the problem is like the previous iphone problem concerning reception when pressure was applied in the wrong place. Possibly the sim card becomes dislodged with pressure. Neither Apple or Sprint seemed to have a real clue. They both wanted me to restore the phone from itunes which I did. Unfortunately, once I did that the sim card was still not recognized and the phone could not be used. 3 weeks for a new phone.
Just letting you all know DO NOT TAKE OUT THE SIM CARD, take it to the store and get it done properly, I just ran into this problem tonight with a new iphone 5 that was literly 2 hours old, I tried every trick outside of taking the sim card out, I went and got a pin but it would not pop out, so I did the logical thing and called sprint, the first lady told me to take out the sim and re insert it, I informed her it was not poping out and i did not want to damage a new phone she said it was the only way to fix it. I said i was using a saftey pin, she said oh no use a paper clip, well I tried two different ones and they both were to big for the hole. so I informed her it wasn't fitting. my wife tried and got it out. but bent the tray in the process.. THEN the lady said oh you need to have the phone off, which would be nice to know ahead of time. So now we turned it off and tried to remove it again and in the process bend it even more.. as my wife is doing this I said "there has to be another way this is bending it" at that point she said let me talk to a supervisor, put me on hold and my wife said now its really bent. then she hung up on me...
So I am pretty distraught by now, I called back talked to a rep that actually took my name and my pin. Then informed me that in no way was I suppose to remove that tray, That they have a proceedure that does not need the sim being removed, That taking back to the store to have them do it was what I needed to do if that had to happen. So I was pretty upset that a sprint rep who probably just looked this thread up and told me to do something that ended up damaging my phone, The second lady has a ticket in and I hope tomorrow when I go back they can either swap it out, or put a new sim tray in it, All i want is a working iphone. Second time I called back they understood I was upset and did a good job to help me, even giving me their extensions but like they said no saying what the store will do for me.
Either way, DO NOT MESS WITH THE SIM TRAY, it is unbelevabley fragile, You are messing with it at your own risk..
Update doesn't work for me, reset network doesn't work for me, nothing seems to work other than turning it off and back on again about 20 times or until it comes back...then the only option is to never turn your phone off. I find that if I don't turn the phone off I don't get the No SIM error at all unless I make the mistake of turning it off again. I went to the Apple store yesterday and of COURSE couldn't get the phone to recreate the error so they said it was Sprint's fault after running a diagnositc on dropped calls...Um - it doesn't drop calls when I have a SIM installed, buddy.... This is nuts. I'm very sadly wishing I hadn't upgraded. .5 inches isn't worth this kind of hassle. Good luck to you and if you find a permanent fix let us all know!
Short fixes such as the network restart and cleaning the SIM only worked up to 12 hours for me. I talked to Sprint and they sent me a new phone. This one has been working fine for three days. It seems like it's either a SIM or phone problem, not a network one. Either way, you'll have to talk to corporate Sprint to get a new SIM/phone.