Read the fine print, most 3rd party sellers will charge you full price if you break any terms of agreement, some of them are 6 months without altering plan, being late, changing phone to different line or replacing an existing account. That is why they can sell em for so cheap, Cuz they snag people in that fashion. If you gave a perfect payment history and are comfortable I would say go for it. If you have any doubts after reading agreement fully, don't do it.