I experienced the same thing upon upgrading my 3GS. SIM not valid. Tried calling Maxis about it, they say that we should restore to stock condition of iOS 4 first before we upgrade to iOS 5. The Maxis technician must be stupid to even suggest that! (Now I know Maxis technicians are stupid)

Only solution for me is to use sn0wbreeze and select "unlock" in the expert setting! That leaves me no choice but to jailbreak it! Really kanas@i larr .....

This post has been edited by jackyyong: Dec 27 2011, 04:44 PM