Last week we brought you the news that Apple had released an update to their iPhone operating system. The update, which was released without much fanfare late on Thursday, was not the looked-for iOS 5.1, nor even iOS 5.0.2, as one might expect. Instead, the software is a new build of the current software, iOS 5.0.1. This meant that instead of going out to all iPhone users, the update has to be deliberately applied. At the time the big story was the fact that Apple had, accidentally or otherwise, left the file system unencrypted. This allowed free access to the software underlying Siri, which in turned paved the way for members of the jailbreak community to port Siri to older phones without breaking Apple’s encryption, and therefore without violating copyright.

Today, however, it has become apparent that there was more to the update than handing Siri to the jailbreak community. According to an article on Apple’s support page, the update apparently fixes an issue with the iPhone 4S failing to recognize its micro-SIM card. Since the iPhone 4S released, some users have been encountering an error where the phone reports that it either has an invalid SIM card or no SIM card at all, or else the status bar shows a lack of service in a well-covered area. The issue appears to have been experienced by a fairly small percentage of users, though for them it was a significant problem. When showing the “No SIM” message, users could not access data networks or make phone calls, essentially reducing their iPhone to a glorified iPod Touch. The latest build of iOS 5.0.1 is apparently designed to fix the issue.

The support page directs users backup and then restore their devices via iTunes, a process which should update the build of their iOS software. There is no word on how effective the update is for those who were having the problem. Many solved the issue by having their SIM replaced, and it is unclear whether Apple has specifically alerted users to the software fix. Meanwhile, the issue created by the unencrypted file system remains. Look for another update in the near future – either iOS 5.0.2 or 5.1 – to re-lock that particular door.