I used Vonage for a couple of years, too, and there are definite downsides. One of them is like all routers, the Vonage router was behind the Comcast modem, and it did a terrible job of assigning the best QOS to the phone lines; when I was downloading a Linux CD, for instance, phone calls absolutely sucked wind.
So, you're thinking, surely that could be adjusted. Me, too - until I tried calling their help service. I had heard complaints about that before, but I blew them off, since I don't mind talking to people with any kind of accent and that seemed to be the main complaint. I also take great pride in my patience; I've been on the "help" end of phone calls many, many times, so I understand the problems. All of that went out the window with Vonage help, though. Asking someone to repeat technical information over and over is frustrating enough, but when they cop an attitude (and they were quick to do so!), too, I'm done.
I switched to Comcast's Triple Play, and they have obviously stacked the deck in their favor. The voice/Internet modem for that is all one unit, and voice gets very high QOS. I never had a problem with any calls or the service - except for the ever-increasing and ridiculous Comcast prices. When my year's tryout was up, I dumped it and went to Skype.
Skype doesn't have any hidden costs: their web page give the whole story right out in the open. It's free with other Skype users, costs a monthly fee depending on where else you may want to call (7.95/month for me to make unlimited calls all over the U.S. and Canada), and a fee for a "phone number". If my PC is off, or if the number rings more than a few times, the calls roll over to my cell. The calls are 99% trouble-free, and if there's trouble, a quick call back will always clear it up. It is now my home office number, and it will be until they jack the rates up to Comcast levels!
Really, in these days of widespread mobile phones, who needs a land-line phone company? After decades of feeling totally ripped off by them going all the way back to Ma Bell, I say good riddance, and bless VOIP! Now if we could just get some real competition in the ISP world... seems to be coming, but I'm getting exponentially older every day and can't wait too much longer!