Some of our customers with factory-unlocked iPhones were having trouble activating their iPhones after updating to iOS 4.3.1 over the past few days. A full restore will not resolve this issue. This is also not an issue with iTunes or Apple’s activation server.
UPDATE: Here’s the possible fix for iOS 6.1 activation problem.
“We are unable to complete your activation at this time. Please disconnect your iPhone from your computer and reconnect it later and we should be able to activate it. We apologize for the inconvenience this causes.”
iOS 4.3 and above no longer supports older version of SIM cards (12-digit ICCID).
Thankfully, there’s an easy fix. Simply put in another SIM (19 or 20 digit) card. Your friends, colleagues or family members may have this type of SIM card. The image above shows a 20 digit ICCID SIM card by AT&T.
If you are based in China and have been using an old SIM card, go to the nearest China Mobile or China Unicom outlet to upgrade your SIM card.
UPDATE: Are you trying to activate iOS 5 beta? You need to register your UDID.