Several companies in Portland are teaming up to offer exactly this.

Comcast has a new plan for $49 that offers a 12mb/2mb cable internet connection along with 4G/WiMAX across the Portland metro area. If you tack on another $20, you get access to Sprint's 3G data network across the country, with the same USB adapter.

It's really a great deal, and you're only paying one company for it. I don't work for any of these companies, but am intrigued by some of the deals that are coming out.

Check it out here: http://www.comcast.com/highspeed2go/