Did you cut it or did they cut it for you?
Neither. It is factory-built that way, specifically targeting unlocked iPhones users who want to use the phone on their network.
Before that, I had cut my original SIM card.
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When you activate it with an AT&T sim, take sim out, and plug the phone into itunes, does it say it is unlocked?
Nope. Just tells me the basic info:
Name
Serial Number
Capacity
etc..