I have an iPhone 3g that was unlocked so I could use any carrier. I accidentally updated it with iTunes and now the phone is locked. What can I do? The phone says I don’t have the right SIM Card and I don’t know how to fix it.
you can try to re-jailbreak it and then you can re-bypass the sim/carrier lock
Turn on Airplane mode and then restart your phone.After that,turn off Airplane mode.Go to settings -->Carrier -->Select your carrier.
Source : - http://forums.macrumors.com/showthread.php?t=761129
You can find a local or online service that unlock it for a fee of usually $2 to $15 only .