When I did my homework, Vonage was #88 on the top100 VoIP porviders list ...
# 1 and 2 were both SIPphones, and I dont like being tied to my PC when I am talking ...
#3 was VoIP.net (now BROADVOX)
I have been with them for 2 years now, and have ZERO complaints ... once every 60 or so calls you get a line with a bit of echo, but hanging up and calling back solves that problem.
The online customer portal is very thorough and easy to use, and support is AWESOME! I think the longest I've had to wait in queue is maybe 3 minutes ...
http://broadvoxdirect.com/ 