What carrier is my iphone locked to?

My cousin updated his iphone to ios 6 and now the iphone is locked. He said that the phone was a gift from his uncle and his uncle bought it from an apple retail store (that's what he says).

From what i know, all iphones that are bought at apple are all factory unlocked therefore it's not possible for it to be locked after updating. So the only explanation left is that his uncle bought the phone from a carrier, and so the phone is locked.

What do you think? Is there any other explanation to that? And how do i find out what carrier is the phone locked to?

Added (1). His uncle said that it was bought from an apple store

Ask the uncle?

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