As a previous sales rep for an authorized reseller for a big cell company (in the US and not for T-Mobile), I have to tell everyone that whenever an authorized reseller sells a phone to a customer, that customer has 2 contracts. One with the cell company and another with the company selling the phone. The cell company's contract is like usual, with the deal about their etf (early termination fee) and the company that sold you the phone has a contract usually stating something along the lines of: if you cancel the service and do not return the phone back within x days, they will charge you for the full (unsubsidized) cost of the phone.
This is normal.. The cell phone company gives the company selling the phone (and contract) money for the contract, meaning if the contract is canceled before x days (I think its usually 90) the cell company doesn't get paid for the phone and loses money. It does suck though because currently, the only company to offer comparable contract-less plans (and therefore no etf) is T-Mobile, but for that to work people need to realize the actual cost of the phones and not be shocked by a $300-$600 phone prices.
Anyways, I'm happy with my contract-less plan with T-Mobile and the amount paid for my Nexus One.