I've had Vonage since 2004. It has worked out very well for me. There are a lot of nice features and the prices are excellent for what you get. The best part is you can take your number with you if you ever move. No more number reassignments because you've moved out your old service area (as is the case with Verizon land line). I've moved a few times over the years, and my number's stayed with me.
Never had any billing or service issues with them. Most of their customer service department is overseas, and whenever I get a foreign rep, they have been the best CS people I've ever spoken to. So I'm quite happy with them.