The contract would likely say something to the effect of "I promise to pay for the data sent to or from this device" and nothing about the owner of the device.

The contract would likely say something to the effect of "I promise to pay for the data sent to or from this device" and nothing about the owner of the device. If anything was said about the owner, it would be that the responsibility of the original contract holder is to ensure the contract was terminated when the sale took place.