I've been using Primus VOIP for a coupla years now, because I need a phone # in Calgary, but I live in BC.
The sound quality is fantastic, and I've had very little downtime due to Primus' fault, maybe 3 occasions.
The best thing about a VOIP box is you can take it with you. I lived in South America for 8 months, took the VOIP, and made toll-free calls to Canada from there. How cool is that?