ooma (www.ooma.com) is anther VoIP service in the US. I just set up a business account with it (not for myself). ooma sells their fancy VoIP router/"answering machine" with a second "scout" router at electronic retail stores (Best Buy, Radio Shack, etc.) for about $250, then one phone line is free for life. "Premium" service with second lines, etc, is $13/ month, unlimited calls to anywhere in the US. You get local area code phone numbers (if you want), but faxing is iffy. Very easy to set up.
They are using Google Voice. Google Voice is free, but only functional for users of the "Grand Central" service so far. Since ooma was all engineered up to use Grand Central, apparently they were in business when Google Voice went public.