Apple has released an update of iOS 5.0.1 which is specially designed to deal with the SIM card issues of iPhone 4S. Previously users have been complaining that they receive No Service and NO SIM card installed messages. Apple requested the users, who are seeing such messages constantly, to download and install this new version iOS 5.
Apple released the newest 9A406 build on silently on Thursday. But at that time they did not specify the issues that this new version is intended to. 9A406 build was pushed to users who did not upgraded to the latest version and users who are already running the newest version has to download it manually from server.
The support pages say that iPhone 4S has problems in recognizing the micro SD SIM card and displays status bar messages like “No Service”, “Invalid SIM”, “No SIM Card installed” or “Searching”. The solution is to download this 5.0.1 (9A406). The instructions are shown in the picture.