https://www.cnet.com/news/samsung-galaxy-a6-and-tab-s4-land-on-t-mobile-friday/

For the Galaxy Tab S4, you have to sign up for a 6GB-or-better T-Mobile Simple Choice or T-Mobile One plan with autopay and it will cost $13.42 a month for 24 months, plus $28 down at signing, after bill credits. That comes to a hardware total of about $350.

Of course, they're limited-time offers, so grab them while you can.