We have had Vonage for over a year now, and the quality of calls is excellent. As too is the service.
It has an answerphone service, and should you have a message, not only is it available on Vonage, but they also send you and e-mail with a WMA file attachment. This means you can listen to the message without having to dial into Vonage.
Plus of course you can call mobile phones. Not a problem here, but with the US system of chopping down your minutes with incoming calls, not a lot of help.
But, as it says, you can call anywhere in the world without burdensome costs. We not only call the US regularly, but also Australia and New Zealand.
Conclusion, well worth the money, and much better than a lot of the Broadband phone packages that come as an integral part of some contracts. We have Orange, but never use the phone, just Vonage.
Unfortunately, we still have to pay BT line rental.....such is life!