This looks similar to Swappa, which I have been using for years to check a phone before buying it or accepting it.
All we need now is a way to quickly check a device for an EIP contract, since the traditional contract is going away. While most carriers are smart and make you pay the lump sum, T-Mobile does not require this. Because of that people think they are free and clear, and then the phone ends up getting blacklisted. If you buy one used, it needs to be free and clear or taken to a store and the seller will have to clear it for you. T-Mobile phones are not safe unless the phone is paid off and you know for a fact.