My experience with VOIP wasnt that great. When it worked, it was fine. When it didnt, I became a tech support middleman between the cable company, the cable modem company, the router company, the VOIP box company, and the VOIP provider. Whichever one you called, it was someone elses fault. Everyone even had a special test to PROVE it was the other guys stuff.
None of them have tech support worth spit.
Vonage took a week to respond to a fairly simple question, although their service worked okay. I couldnt get a LOCAL local number from them though, just one from an exchange about 40 miles away.
AT&T Callvantage actually worked for nearly a year with practically no problems. Then the box started making the phone ring once in the middle of the night about 3-4 times a week. Turns out that when the box reboots or loses its connection, it rings the phone. Swell. After a week of tech support "its your cable connection/cable modem/router/anything that isnt us" and hours of running various tests, I found an internet posting that said the problem was in the new firmware that went out to the boxes to enable E911 service...and gosh...thats exactly when my problems started. I emailed the callvantage tech and told him what the fix was (a newer box from a different manufacturer with different firmware)...he never replied. So I cancelled.
Went with Sunrocket, figuring hell, if it doesnt work at least its cheap. It didnt work. Lousy call quality, all sorts of problems getting busy signals when the # we were calling wasnt in use, people calling us when we werent on the phone and it went straight to voicemail or rang busy. Although both vonage and callvantage worked fine with the same 'setup', I went through several weeks of having new cable wire pulled through the underground conduit to my house, bought a new router and cable modem...and had the same problems. Seems some of Sunrockets "local access partners" rent them the crappiest crudball barely working equipment and dont maintain it. So some people in some areas have fantastic sunrocket experiences and others in other areas dont.
So the summary is: if you're a technically proficient person that doesnt rely on their "land line" for business, important calls or emergencies...give it a try. Whether you fit this criteria or not, the minute you have a problem...good luck to you.
Oh yeah...and its real fun once one of these outfits gets their hands on your "local number" via porting. Took 5-6 weeks to get vonage to release it to callvantage and 2 months to get callvantage to release it to sunrocket.
Oddly...about 30 hours for AT&T/SBC to get it "back" from sunrocket. Guess they had a bigger stick.