I predict that dedicated mobile broadband plans with their own USB modems will disappear in favour of ordinary mobile phone plans and occasional tethering, at least for domestic applications. There are only a couple of situations in which dedicated mobile data at 3G speeds comes in handy, and they overlap completely with mobile phone usefulness. It's going to become an increasingly hard sell, which is why most providers are attempting to prevent you from tethering your phone unless you pay extra. With today's phone plans and included data, they suddenly have a stockpile of absurd, outdated wireless modems they either need to sell or write off. And since they have near-total control of their wireless networks, they're choosing to impose restrictions to upsell you on the tethering option, or get you to buy dedicated mobile "broadband" while that still sounds halfway sane.
Mokalus of Borg
PS - In my first month of an internet-enabled phone plan, I've used less than 100MB.
PPS - That might be just me.