A signal problem with the iPhone 4S
Several iPhone 4S users have reported experiencing a signal issue that affects both iOS 5.0 and 5.0.1, although the problem seems to be primarily with 5.0.1. The below steps may help you resolve the issue.
1. Go to Settings-->Phone Menu-->Turn SIM PIN off. You will be prompted to input your PUK code. You can access this code via your AT&T account.
2. After inputting your PUK code, return to Settings, and turn the SIM PIN to off.
3. Turn airplane mode on. Wait 15 seconds before proceeding to the next step.
4. Go to General-->Reset Settings-->Reset Network Settings to reset the device's network settings.
5. There is a chance that upgrading to iOS 5.0.1 destroyed your SIM card. Visit an AT&T store and ask that they test your SIM card. Some people have been able to get a new micro SIM card this way.
6. Download the latest 5.01 from iTunes once you have your new micro SIM card.
7. Restore your phone to its factory settings using our guide on how to do so.
8. Follow Step 1 once again to turn the SIM PIN off.
9. Open Settings-->Carrier-->Automatic. Turn automatic off, and manually select your network.
I hope these steps have fixed the problem for you! As you can see signal triobles can be solved completely. So sell your iPhone is not necessary.
You can leave me a comment if you need any help.
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