I use one for a land line. It's stupid cheap and perfect for how little it gets used. Just keep in mind that you probably want a high bandwith connection. It seems less efficient than skype or something comparable.
I have been using it since it first came out with very little issues with the first version no issues with the second version. A good fast PC & connection helps a lot. My biggest issue is that it will automatically shut off after an hour and a half. Sometimes I need to do a reboot if I haven't shut my PC down in a week or more....other than that it has saved me a lot of $$$.
My fiance used this service when she was in Guatemala on a mission trip. Without it I don't think we would have been in touch because it was the only service in the village. I'm thankful for it and even though it would drop our calls every now and then it still got a few "I love you/miss yous" in.