Several people have reported a problem in which iPhone 4S drops the network, preventing them from making calls, sending text messages and/or accessing the internet. It has also been reported that resetting network settings is not fixing the issue. Turning the iPhone on and off fixes the issue for a short period of time but then the network is dropped again. However, it seems that disabling SIM PIN solves the problem, that is, until Apple finds a permanent resolution. To disable SIM PIN:
- iPhone: Settings > Phone > SIM PIN > slide the SIM PIN to Off.