MetroPCS has a deal for a free year of Amazon Prime and a free Samsung J7 prime phone when you port in a line from another carrier and sign up for the $50 unlimited data plan.
https://www.metropcs.com/amazonprimeonus.html
MetroPCS is a prepaid brand of T-mobile for those not familiar with them.
If you don't want to stay with them for phone service, there's no penalty to drop the service after redeeming the Amazon Prime offer and keeping the phone as a mini tablet.