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?
The "subsidies" are not truly subsidies, they are built into the contract prices. At least in the EU every operator offers SIM-only contracts (though they may or may not advertise them), because not doing so would be a clear and blatant violation of EU anti-tying regulations, and they are always cheaper.
To the extent you are getting a real subsidy, it will be if the carrier decides to forgo margins on the device.
This isn't always true, though it's typically only not true when operators are throwing ridiculous offers at people who are trying to leave them. Similarly, I got phone a few years back at a ridiculous student-only deal. Both cases ended up with me paying about £200 more over the whole contract than I would've with SIM-only contracts, and both got me phones that retail for more than double that.
For any bundle they are offering they should have a non-zero cost in acquiring the phone, in which case they'd have a very hard time to justify not letting you sign up to an unbundled agreement where at the very least the cost of the phone is removed. They'd almost certainly be breaking the law if they do (of course that doesn't necessary mean they aren't doing it though)
