I bought my new 4S on day 1 preorder and installed the new IOS 5.01 that day it was available (Oct 2011), both without
problems. In the past 4 days, the 4S has lost the VZ signal and a popup says "SIM Failure". As far as I know, my new 4S does not have a SIM installed since I said NO to the global option. I even tried opening the SIM drawer, but it would not open.
I tried every fix available, and the only one that worked was a power off or soft reset (power + home). But these fixes
only worked temporarily 2-3 hrs then the SIM fail reappeared and my 4S said no signal, while my other iphone (version 4) with the same IOS said strong signal.
Found this new fix on the apple website, which works. I have not gotten a "SIM Failure" going now going on 48 hrs and no loss signal!!
-Synch your iphone with your PC using the latest iTunes (10.2), and get a backup (should backup automatically)
-When synch is complete and iphone still connected via USB, hold down the power button + home (like a soft reset0. After 8 sec release only the power button. You should get a popup that the iphone is resetting to factory settings, and telling you that you must restore the iphone
-Now, select restore to previous backup (not new phone) on your iTunes screen. iTunes will grab the latest IOS build and other items (like modem firmware version-mine changed to 1.0.14 from 1.0.13) from the apple website and restore your phone to the backup (takes a while dependent on your PC speed, my Win XP took 20 min)
-When restore is complete, synch your phone again and it will reload all your music, apps, tones and photos.
Now enjoy your iphone in peace!!