T-Mobile can stack all all they extras they want but I don't see myself changing my current plan with them for some time, if ever, unless they force me to.
I managed $100 for 2 lines back in March 2017 when I switched from AT&T to T-Mobile and got in on the 20% Friends & Family discount meaning I get 2 unlimited lines for $80 a month, (Which gets knocked down to $72 or $64 respectively if I manage to stay under the 2GB Kickback limit, which is something that doesn't happen too often--though I've admittedly stopped trying recently.) which is the cheapest I've seen of any of the major carriers, unless I've missed something.