Originally Posted by FallOutNerd
Were you answering my question? If you were, thank you! I just have to buy the unlocked version and load my sim card, correct. I was planning on getting the t mobile one or the unlocked.
Yes, that is correct.
That's actually the whole point of the SIM card - it identifies you to the network, and any phone you put it in becomes "your phone". The only thing to watch is that a phone bought from a network will almost certainly only accept that network's SIMs. So a T-Mobile or unlocked model should be fine (check 3g/4g frequencies on the unlocked model match T-Mobile).
I last bought a handset through a contract in the 90s. Since then I've just bought offline phones and transferred the SIM.