i have been using onesuite for over a year now. never had a problem with them .
Altho i get busy tones once in a while, long distance calls are clear. No hidden charges etc.
I also use it occasionally for international calls. Have called Uk (4.5 cents) Singapore 6.9 cents and India 35 cents. they recently upped the rates to India to 45 cents.
Voice quality seems pretty good so far. I think they have some promotion where if you spend $20+ every month they mail you your voice messages.
Best is the zip dial feature. You can program upto 4 phone nos so that you dont have to dial in your pin.
Da_scud