May be I am missing something (I am not in the US). But, do you have to pay rent for the device if you go for the subsidised option? If so, then its not a subsidy. If it is a subsidy, then you are clearly gaining the subsidised amount. The only thing that you are losing is the ability to switch carriers for the contract period. Also, are you not allowed to choose a plan of your choice if you go for a subsidised phone?