https://www.cnet.com/news/t-mobile-cyber-monday-deals-are-live-get-your-free-iphones-galaxy-lg-and-oneplus-phones-now/

If you're confused about how the bill credits work for phones that have $750 knocked off from their price tags, here's an example: Say you purchase a $900 phone and receive $250 from the phone you trade in (again, the device needs to be eligible). On top of that $250, you'll get $500 in credit across 24 or 36 billing cycles.  

Some of the phones you can get include: