I have a similar problem with my iPhone 4S running iOS 5.0.1. However, the problem seems intermittent at best and not easily reproduced. I'll do my best to explain.
My network coverage at work is terrible and I rarely get any service when at work. However, the moment I step outside I can get full 3G signal, even with my old 3GS. Therefore, I place my iPhone into Airplane Mode whilst I'm at work to conserve the battery. Occasionally, when I deactivate Airplane Mode once I get outside (note the previous statement of full 3G signal) the phone says "Searching" for about 10 seconds, then "No Service". If I try to turn Automatic Carrier Selection to "Off" during this time, I am returned to the Settings main menu (NOT the Home Screen). If I restart the phone and unlock my SIM it returns to normal operation. This leads me to believe there is a software bug somewhere.
I also use Airplane Mode overnight to allow me to use the alarm function whilst conserving the battery. However, this fault does not seem to occurr at my home, only at my place of work. I suspect this may be a combination of faults with that particular mast and a possible software fault, as I did not have this problem with my 3GS or 4S running iOS 5.0.
I will attempt to supply Apple with this information in the hopes that they can uncover any bugs that may be present in relation to this fault. I hope, for all our sakes, this can be rectified soon!
I may have found a solution! First, if you are having these problems, check the build of your iOS version. Go to Settings>General>About>Version. This should read 5.0.1 (9A405).
Upon closer inspection of search engines, I came accross a website titled "What is the difference between iOS 5.0.1 build 9A405 and 9A406?". As it transpires, there's a great deal of difference, for us 4S users anyway.
Here's the website (I hope I'm not breaking any rules by posting a link. Please let me know if I am!):
The difference between these builds seems to be a fix for a problem in the iPhone 4S not recognising SIM cards. Apple's own knowledge base article states the following;
"In certain situations, iPhone 4S may have difficulty recognizing a micro-SIM card, resulting in the following behaviors:
"Invalid SIM" or "No SIM Card installed" alert appears intermittently.
Status bar displays "No Service" or "Searching" in a location with good network coverage."
Apparently, because this is a small fix for a small number of users, the fix has not been released as iOS 5.0.2. Therefore, people who updated to 5.0.1 early, such as myself, can't simply update by checking on iTunes or Software Update. In order to receive this newer build we have to restore the phone to factory settings, confirm the build has been updated to 9A406, then restore from a backup.
I haven't attempted this yet as it may take some time, and I don't have enough until later in the week, but it anyone else tries this beforehand and finds it works, please let us know!
I followed the steps from the link in the previous post (http://support.apple.com/kb/TS4148) and it solved my problems. Like Icelighter, I work in a building where I get at most 1 bar of service, often none. So I use airplane mode. When I would take it out of airplane mode, about half the time no signal would be picked up, even upon walking outside for a while. I had to restart the phone then it was fine. By updating the firmware to 9A406 as described in the link above, it solved the problem. Everytime now it picks up a signal real quick - usually a better signal too!
Note: if you haven't restored like this before, it takes a little while. As I recall it took about 30-45 minutes to (a) download iOS 5.0.1 on my computer, (b) for the phone to reset itself, (c) to reinstall the OS, and (d) restore my backup [all done via the steps in the link above]. So make sure you have a little time. Also, this doesn't include the time it takes to re-add all music and video. (Installing your backup only includes apps, messages, contacts, settings, etc.
I too have managed to update to 9A406, and while it rectified the problem at first, it returned soon after. However, it has only happened once since I updated.
I've also managed to find a pattern! I've found that the only time the problem has reoccurred is when I've activated Airplane Mode when I've had no signal. I have NEVER had the problem since updating to 9A406 and activating Airplan Mode when I've still had signal, and I've been attempting to determine this for quite some time now!
Perhaps this information can help solve the issues raised, or at least help those who are currently affected.
ginney pig? wrote:
searching, connect and then "no service" after airplaine mode deactivated in iphone 4S. And phone service killed in standby after a longer period. Nothing wrong with data yet in standby. Otherwise, telephone ability ok.
Resets network and os did not work. I suspect software problem. Tired of sitting in lines.
Have you tried resetting you network settings. This seem to fix a lot of problems. Go to Settings/General/ Reset(Last Option) Reset Network Settings. A Hard Reset may do it to. Hold Power and Home Buttons until the Apple Logo appears, let go when it appears.
Hope this helps.