I bought my new iPhone 4S last October, no problems until I updated to iOS5.0.1 software version, my phone began to appear "NO SIM INSTALLED" every day at the mornings, a frequently signal loss every moment, all day, the signal marks at full bars and 3G appear on screen, but no signal, need to have restart the phone every time I wanted to make a call, and after that no signal again, a lot of lost incoming calls, mesages too, my iPhone was an expensive iPod for a while, i tried restoring my phone, changing for a new SIM, ... nothing, but searching in this forum I found that issue, so I decided to update to iOS5.1 Beta 3, and, surprise !, I have my iPhone back, NO PROBLEMS since last update, ALL IS OK UNTIL NOW, I´m a happy guy at now.