T-Mobile has add a line and get a line free on family plan magenta plan. Check scrolling page slightly down. 4 lines for $140.00. Tax/fees included. This what I was waiting for.
Possibly combine with any Costco offer. Especially iPhone $700 get back offer will make it a super sweet deal.
Note: deal is for magenta but I was able to get it on my current T-Mobile One plan. 2+2=4 lines now.
Full terms from T-mobile site.
Choose your lines. See what you'll pay.
Select how many lines you need to see what your monthly rate will be. Taxes and fees are included, so you'll never pay a penny more for Magenta.