I am pushing the affiliate program but I won't put the ref code here.
www.voipo.com. Yes, they are affiliated with Hostgator so I know some people will not even take a look.
I have been using the service for a while now. Call quality is amazing. Prices are dirt cheap. I have used several voip services and this one is bar none the top as far as call quality. There are also a bunch of extra features you can access through the admin panel if you are a telephony freak.
Check them out if you are in the market. This is an honest plug from a current user.