Currently Being ModeratedJan 24, 2013 1:44 PM (in response to florcostigliolo)
You posted in the Older Hardware (hardware prior to the year 2000) forum instead of the iPhone forum. To get answers to your question, next time post in the proper forum. See https://discussions.apple.com/index.jspa I'll request that Apple relocate your post.
Currently Being ModeratedJan 24, 2013 1:54 PM (in response to florcostigliolo)
Are you sure you have 6.0.1 on an iPhone 3G?
If you do, some sort of hack was involved since 4.2.1 is the
latest that will run on a 3G. And hacking the iPhone to
install unauthorized software causes all sorts of problems,
including failure to activate.
Has your iPhone 3G been hacked/modified/jailbroken?
Which version of Cydia are you using?
Currently Being ModeratedJan 24, 2013 2:00 PM (in response to florcostigliolo)
Most likely, that's because your phone was previously hacked to carrier unlock it, and when you updated the hack was removed and the phone re-locked to its original carrier. It will now activate and operate only with that carrier.