I've had it for about six - seven months. I have not had any problems with the service (vonnage) and the cost is very inexpensive. However, since I hardly use the phone, I have just canceled my account today and I'm just using my cell phone. But if you need/want a home phone, I highly recommend vonnage. Just a side note, I have the 3mb cable service. If you have the slower speed broadband, I'm told you may experience some static or dropout.
I've saved a few customer accounts by turning on QoS (Quality of Service) or Bandwith management in the broadband router. Modern voice codecs use between 8 and 64 kbit so theoretically you could use a dial up connection in some cases and simple broadband connections (128kbit or 0.5Mbit) should give you perfect sound quality without dropouts. Actually most often its not the connection speed thats the problem. Dropped packages and lags are worse. One of the simplest tests you can do is to ping your ISPs gateway (try "ping gateway ip -n 100" and look at the statistics when its finished), ideally you should have zero dropped packages and a low result for the maximum time. If there are package drops call your ISP and complain (you'll have to spend a few minutes explaining that it isn't the speed your complaining about but the quality they're just not used to people that complains about anything else than the speed).
I sell VoIP phone systems...I should clarify VoIP enabled...the majority of the companies that buy http://www.carrollcommunications.com/phone_system_ipoffice.html this dont utilize the high-end apps... Maybe its just the people I sell to...my company does not do enough volume to have much more than anecdotal evidence.
either really not to fussed where there based just want to compare services available to use within the uk