I was a Vonage user for 5 years, overall I was happy with the service until recently, I think my adapter was on its way out. To be honest, in the five years I had vonage I don't really recall a time when it never worked, in fact, dare I say it was more reliable than my old POTS service.
Started researching new adapters, Vonage made a decent offer for a free one, but then I'd have to recommit to another 2 years, something I didn't want to do. They also just raised their prices on the low end plan, bringing my average monthly cost up to around $24 w/ taxes. Ended up coming across OOMA on Amazon, $200 for the box, no monthly bills, 3000 minutes a month. Its a Peer to Peer phone service, it calls out using other people with OOMA's home phone line (those that kept their local service). They don't have to pay for switching (like Vonage and the other VOIP's) so they can get away with offering free service. Arguably its not the safest (using other people's lines) and the box is only good as long as the company stays around, but my break even point is about 9 months, so as long as they stay around at least that long, I'm golden. Anything after is just icing on the cake as I don't have a phone bill any longer.
So far i've been VERY impressed with OOMA. Sound quality is noticeably cleaner than Vonage and the Ooma box itself is just pure sex. I've got mine going through a Wireless Bridge about 20 feet (and a different floor) away from my router and it works like a charm. I was also happy that I was able to snag a kickass phone number when I signed up last week (ends in 1001).
Anyway, I'm still new to Ooma so I can't give a full lengthy review, but this far its been quite impressive. Enough so that I'll likely cancel Vonage all togeather at the end of this month (right now its just forwarding to my Ooma)