We attempted something like this. The only issue we had was places that offered free wifi, but wanted you to login on a redirected splash page, before they'd allow you out to the interwebs. The phone had no way to do that, so in those places was unable to be used.
I've got an iPhone, so have been doing this with a sip based app called iSip. Because I can log into splash pages, it works pretty well for me.
