I think the MVNOs, combined with smart phone market penetration, are the real driving force removing 2 year contracts. People aren't so bad at math that they won't eventually figure out that $200 (or less) + 24 * $40 is less than 24 * $60.

I guess the price point on good enough smart phones is also at least headed below $300 (for me it's less than $200, but people like shiny things).