One reader contacted AppleInsider on Thursday to share their frustrations with error messages that read "Invalid SIM" and "SIM Failure" on their iPhone 4S. This person said the errors began occurring after they updated to iOS 5.0.1, though other users posting on Apple's official Support Communities website, in a thread with more than 30,000 views to date, have experienced similar problems since the iPhone 4S first went on sale in October.
"This problem can only be solved when you reboot your iPhone," the person, who is an AT&T customer, wrote in an e-mail. "Everything else fails — restore, removal of the SIM, etc."
When users experience a SIM-card-related error, basic functions including making phone calls, sending text messages, and using mobile data become unavailable, as the handset cannot make a connection with the wireless data provider.
The iPhone 4S is a "world phone," which means its redesigned antenna and internal components are compatible with both CDMA and GSM carriers. Micro SIM cards placed in the iPhone 4S are only used by GSM carriers to identify a subscriber and grant them access to a carrier's wireless network.
But while only GSM carriers, like AT&T in the U.S., use the micro SIM slot on the iPhone 4S, users on CDMA carriers, like Verizon and Sprint, have also reported experiencing SIM-card-related errors. iPhone 4S units sold through CDMA carriers come with a "roaming SIM" installed, which allows CDMA customers to roam worldwide on GSM networks.
"No service on my white 32 GB 4S on Verizon," user 'racyb' wrote in October. "Did a shutdown and reboot....it went into searching mode and finally found Verizon again after 1 minute. What is going on?"
Since the release of iOS 5.0.1 earlier this month, another thread at the Apple Support Communities website features more users who say the problems began occurring after they updated their iPhone 4S. Some say their iPhone displays full signal reception, yet error messages like "Call Failed" and "Invalid SIM" continue to display.
"Same problem here in Brazil," user 'GuiMedrado' wrote on Wednesday. "Bought my 4S - 32GB unlocked in Switzerland and couldnt' make it work after upgrading to 5.0.1. Any solution?"
The iOS 5.0.1 update was released earlier this month in an attempt to address battery life issues reported by some users. But some battery-related problems have remained, and Apple has publicly said it is still working to fix those issues.
One rumor this week claimed that Apple will issue a new update, iOS 5.0.2, no later than next week in a second attempt to improve battery life with iOS 5. There was no mention of any fixes for SIM card issues or error messages.