Like most carriers, timing is everything. Your best deals are typically during a limited time promotion. I got in on a ONE Plus Promotion in March of last year with a bunch of stackable discounts. I currently have 11 voice lines and an Apple Watch LTE line. My monthly bill is $185 with no taxes or junk fees. That is with unlimited service, 10Gb tethering, 256kbps international data roaming, free Canada & Mexico, 1 hour GoGo, etc. on every line.

BTW, that article in Forbes seemed wrong about T-Mobile ONE for Canada & Mexico. As I recall, the basic plan has free high speed (5Gb) data and all the other stateside features included without any additional fees or add-ons.