Makes no sense to you?
Cost of iphone unlocked - $699
Cost of iphone on contract - $199
Difference = $500 = amount the carrier subsidized your purchase
Early termination fee = $350
(for most US carriers that carry an iphone, for their smartphone plans)
So, if the subsidized phone came unlocked, you could:
(1) sign the contract and buy for -$199
(2) break contract, pay early termination fee -$350
(3) sell iphone for +$699
(4) net profit +$150, at the expense of the carrier
Most carriers let you unlock the phone after you've owned it a few months and pay your bills on time, in order to avoid the above scenario.
Otherwise, why would they let you just take $150 out of their pocket? If you were the carrier, would you let that happen?