I had absolutely no problem switching over to the unsubsidized, contract-free account, took less than 5 minutes over the phone, but they did tell me the same thing about not being able to go back to contract.
However, another friend of mine did the same thing, then decided he wanted to go back on contract. He called them asking for it and, when they declined, said he wanted to cancel and go for another provider. They routed him off to the retention department who apparently do have the authority to get him back on the contract plan and did so with minimal fuss. Of course, YMMV, but it worked out just fine for him. In the meantime, I'm still saving money over two years by going non-contract.
However, another friend of mine did the same thing, then decided he wanted to go back on contract. He called them asking for it and, when they declined, said he wanted to cancel and go for another provider. They routed him off to the retention department who apparently do have the authority to get him back on the contract plan and did so with minimal fuss. Of course, YMMV, but it worked out just fine for him. In the meantime, I'm still saving money over two years by going non-contract.