I have had it for about 5 months now. I love it. Once I got all of the settings set up properly I had no more dropped calls or static. The only thing that does suck is minimal amount of phones. I just went and picked up a set of those Vtech phones that all piggy back off the primary base and now I'm good to go. And it's inexpensive as hell. I'll be happy to answer any questions that you may have. Or at least try to answer what I can.
I have vonage. I use it for both faxing and voice. The feature list is impressive and the call quality is acceptable most of the time. My connection is supposed to be 512 up and up to 3.5 mb's or something down (never is) cable connection.
Some problems:
before I bought the expensive upgraded cable internet package it was hard to send a fax on medium speed. It worked maybe once out of 3 times. Recieved faxes have always come through. With the slower cable speed call quality was hit or miss. Now it's great. I havent tried the softphone to see if it is worth it.
My son has it. Unlimited local, regional and long distance calling, $27 a month, total.
You have to have cable internet, it's a PITA otherwise.
In the six months he's had it there have been like three problems, involving difficulty answering or just the line acting wonky. Honestly, though, not any weirder than a cell phone, though.
Multiple extensions are a hassle unless you're comfortable with cordless phones. Since he only has the one phone in his dorm room it's not an issue ...