Choosing a VoIP carrier—more than just price
Two of the most important features to look for when choosing a VoIP carrier are support and call quality. Usually, once you set up and everything is working, you won't need support. I always tell clients that there is no "boxed" solution that I can sell; every installation is a little different. Internet connections are all different even with the same provider. If you have a rock-solid T1 or something better, then this shouldn't be a problem. DSL seems different from building to building, even in the same area.
So how do you test support before giving them your credit card? Call them! Try calling support at the worst times, such as Monday afternoons when everyone is back to work and online. Also, try calling after business hours. See how long it takes to connect to a live person and if you can understand them once you speak to them. Find out where their support is located. Try talking to them and tell them you are thinking about signing up...