so what exactly triggers the "iphone is activated" message?

i know a successful OTA does it, because that happens when i OTA a iphone that is flashed to page plus.

but i cannot OTA a cricket, guess it is because of my area.

i know there are verizon or sprint iphones that will activate itself even without OTA, i guess that is because they still have a number associated with them some how.

but if the phone doesn't activate itselt, or if i cannot do the OTA, the will just stuck at a "unactivated state". i can still talk text and web, but mms usually have problem in this state (i am not sure if it is 100% related).

what can i do to a phone in such un-activated state?