The $40 unlimited plan would seem to either not exist, or be this 2Gb plan with reduced speeds after 2Gb: http://www.t-mobile.com/shop/plans/mobile-broadband-plans.as...
Last night, I determined an hour of netflix on my at&t nexus is the better half of a gig, and twice that on a xoom lte I am testing. 2Gb of data is nothing -- but that does seem to be the $40 "unlimited" plan, in which unlimited means throttled speeds after 2Gb.