Right now we have 2 lines on t-mobile under the old plan ($80 for 2 lines, 2 gig data each). including tax that's $89.
If we switch to the new plan, it's on sale for $100, including fees. AND t-mobile does a buy-back of $10 if you stay under 2 gig. We rarely go over 2 gig/line.
So at worst, it's $10 more/month. At best, it's $80, including fees. Which saves us $10.
(of course, under the old plan, most of the music streaming apps didn't count towards the data)