No, the carrier does not "own your phone"--they're taking a risk that you'll abide by the contract.
Even if you get out of your contract early, you have to pay a termination fee, which is effectively the remaining part of your carrier subsidy. AT&T is going to get their money one way or another.
Also, going to Europe for 2 weeks doesn't mean you stopped paying your AT&T bill for those weeks, either. It's perfectly reasonable to expect your phone to not be carrier locked.
I wasn't clear. I didn't mean the carrier literally owns your phone. I prefixed with "I believe" intending to convey how it seems to work, not the technical fact. I should have written, "It's as though the carrier owns your phone".
Even if you get out of your contract early, you have to pay a termination fee, which is effectively the remaining part of your carrier subsidy. AT&T is going to get their money one way or another.
Also, going to Europe for 2 weeks doesn't mean you stopped paying your AT&T bill for those weeks, either. It's perfectly reasonable to expect your phone to not be carrier locked.