I had reason to pick up a couple cheap pre-paid phones at a gas station once. I wasn't asked to give an ID to anyone to buy them, but once I had them I needed to call a company to activate the phone and they were very particular about what phone number it would work from. It had to be a landline. Payphone wouldn't work. My work phone didn't work. It was difficult to track down a phone line they'd accept and even then one of the phones refused to register.

It seemed to me like they wanted to make sure they could tie the phones to an individual through activation.