they can't file lost/stolen ESN, since you "legally" own the phone now.
they can't claim that the ESN that you purchased, to "turn in" for 3rd party insurance, will work because at the time, the ESN was clean/free, then activated on your line (so you assume ownership)
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with that being said, i'm curious to see what happens to all the GSM phones now.
ESN (CDMA phones) were always checked before it could be activated.
there are people walking around with stolen GSM AT&T iPhones being used on either AT&T (another account) or T-Mobile. what happens to them, ever since the 11/1/2012 change?