Towards an upgrade? I don't know of a single US carrier that actually offers a discount for upgrading. I see only the following three options
- Pay full price, which doesn't count "towards an upgrade" since you can do this every day if you please
- Pay full price - $xxx dollars for turning in a phone usually worth close to that anyways. Again this is not an upgrade option as most carriers allow this unlimited times because they profit from the trade-ins.
- Switch and save, in which it doesn't go towards an upgrade but still usually requires handing in a phone. This usually results in a large bill to pay the phone off
Verizon, ATT, Sprint, TMobile all don't offer subsidized pricing anymore, I have checked ad nauseam. The closest you can get is option #2 or #3.
On a separate note unrelated to the quote above, once paid in full from Sprint or Verizon they will unlock the device. Some people say it is difficult, but I have never encountered any issues having it done. Additionally the FCC applies heavy pressure to service providers to unlock fully paid devices.