Sprint tried that in the San Jose area I think a few years ago using MMDS (Multichannel Multipoint Distribution Service). Wasn't terribly successful. Perhaps the time wasn't right then.

I recently read somewhere that Intel, AT&T and someone else were putting together a joint effort to provide nationwide 802.11b/g service. Something with fairly wide coverage (don't know how they'll do this), unlike the T-Mobile access points in airports, Starbucks, etc.