Fixing the iPhone 4S Signal Problem

The iPhone 4S "No Service" signal problem is characterized by not getting any cellular signal coverage but  can still connect to Wi-Fi

The iPhone 4S "No Service" and "No Sim" Problem 

 My brand new iPhone 4S showed a noticeable cellular signal problem - the network connection keeps dropping out randomly. I noticed this immediately after activation. The signal cycles from full bars to "No Service" without any apparent trigger. When I was troubleshooting I found out that even when there is full signal, calls and text messages from another phone may in fact still not get through. I was sure that it wasn't a sim card problem because the sim card works fine when I inserted it in other phones. Furthermore, I noticed that forcing the iPhone 4S to resend a failed message or reconnect a failed call pushes the signal down to zero. This cycle happens more than 20 times a day: full bars, to "Searching...", and then "No Service." Restarting the phone fixes the signal problem temporarily but then why would I have to restart my phone 20 times a day just to make it functional? I have also observed that when my iPhone 4S is idle, it somehow loses contact to my sim card and thus the "No Sim" error. "Reset All Settings" does not solve both of these problems for good.

The iPhone 4S "No Sim" problem happens when your phone is idle. iPhon 4S seems to lose contact with your sim card.

Apple's solution: iOS 5.0.1 (9A406)

I did a lot of research and found out that Apple released an iOS 5.0.1 build (9A406) intended to address the iPhone 4S signal problem. A build is not an OS upgrade. It is like a repackage of the same firmware version with an inclusion of a patch that addresses a "minor" problem. In the contrary however, this problem is quite big - several users allover the globe are talking about this issue (Check out this thread at Apple Support Communities). So when I checked the version of my phone's firmware, it was in deed iOS 5.0.1 (9A405). So I went ahead and upgraded, and the problem hasn't resurfaced since.

I noticed in several forums that people complain about the build not working properly. Or that the build loses effect after 24 hours. So to answer that, the first statement may be true. I work as a product engineer in an electronics company and it is possible for a problem to be common to a set of devices but not to all. So a "build" or solution developed to target the problem surfacing in a one set of devices may not work for the other sets. In order to come up with the correct (comprehensive) fix, the commonality of the failing devices have to be correctly traced and identified. Only Apple can do that since they have the complete record of all the serial numbers, models, IMEIs, and modem firmwares of all the manufactured iPhones. The second statement however does not make sense to me. A software fix does not have an expiration date. It's either the fix did not work at all (which means that the observations saying that it did temporarily in some phones maybe be inaccurate), or something other undocumented condition in the iPhone is going on that's causing the problem to persist. Below is a step-by-step tutorial on how to check if the 9A406 build will work on your phone.

Step 1. Check your iPhone 4S firmware version. On your phone go to Settings > General > About > Version (see screen shot below). If the version says 5.0.1 (9A405) or earlier and you're experiencing the signal problem described above, then your phone is a candidate to the 9A406 fix.

Check your iPhone 4S firmware version to see if you can upgrade to the iOS build 9A406 if it isn't already.

Step 2. Connect your iPhone 4S to iTunes and backup. On the left sidebar in iTunes right-click on your device (name of your iPhone) and select "Back Up" (click screen shot below to zoom in). The backup procedure will create a copy of your phone's contents and settings to your computer. This step is extremely necessary because Step 3 will erase all contents and settings from your device. Once "Back Up" is selected, the top portion of iTunes should show these statuses: "Backing Up" and "Syncing".

Right click on iTunes Devices and select Back Up to back up your iPhone 4S contents and settings to your computer.

Step 3. Restore. Click "Restore" in the Version panel in iTunes and this will prompt you to Back Up. You can select "Don't Back Up" because you have already done that in Step 2. A second dialog box will then prompt you if you want to restore your phone to its factory settings. You go ahead and select "Restore". This action will download the latest iOS build from the Apple server and install it to your device. This could take a while, depending on your internet connection speed. Click Accept when the Installation End-User License Agreement appears so the installation will start. 

Click Restore Factory Settings in iTunes to start downloading and installing the latest iOS build on your iPhone 4S.

Step 4. Restore from Back Up. When the installation completes iTunes will ask you if you want to Restore from Back Up or treat it as a new iPhone. Restore from Back up will put all your previous contents and settings back to your device. If you select treat as new iPhone, you will have to perform iPhone activation from scratch. Select "Restore from Back Up".

Step 5. Confirm firmware version. When data and settings restore completes, you'll see your iPhone's latest firmware version  when you go to Settings > General > About > Version. Your iPhone 4S signal problem should already be fixed at this point.

My iPhone 4S has been running smoothly for over 7 days now. Let me know if Apple's 9A406 build worked for your iPhones as well.