I 'upgraded' my 8Gb 3GS to ios5 and it got as far as activation. However, the phone refuses to acknowledge the fact that a SIM is present and therefore refuses to activate. I'm in the UK and have tried both o2 and GiffGaff SIM cards with no joy. I managed to downgrade back to 4.3.3 (which it was running previously) and it's STILL saying no SIM! There's a massive thread about this on the Apple forums: https://discussions.apple.com/thread/3374731?start=0&tstart=0 People all over the world with the same problem and almost all of them have a 3GS. I bought my iPhone second hand and it was already unlocked and jailbroken, but there's loads of people on the Apple thread that have the same problem with locked and un-jb'd phones. What the heck is wrong with this?! I'm incandescent with rage that I've been without my phone for over a day now because of this - I'm a freelancer and need my phone for business. GET IT SORTED APPLE!