agreeing to the conditions that come with it?
"If you buy a mobile phone, or any other kind of product, you agree to the conditions /contract that it came with.
If you buy software, you could easily duplicate and distribute copies (free or for a fee), but the agreement forbids that."
Except that we all know that a lot of the time companies use terms in their contracts and EULAs which will never stand up in a court of law. Maybe it's different in the States, but here our consumer rights take precedence over any rubbish a company hopes might frighten cutomers into doing things their way and their way only.
The Plan is only a part of the contract and the payment side of the contract, ie: the consideration, is another. As long as the user honours those parts of the contract which are important legally on their side (the consideration) then I see few reasons for objection which'd actually hold up.
Your house analogy is just irrelevant when we're talking about people buying a product and paying for it as agreed, but deciding to use it in a different way.
If you buy it, it's yours to do with what you want. Company control stops once they've got my hard earned readies.