Vonage has been my only landline since Oct 2002. I completely cut the cord with Verizon and went with cable net and Vonage for the phone. It's been great, and the few times when there's been any kinda problem or question, they've responded rapidly via email or phone support.
I have the ATA on the same UPS which powers my cable modem, in case of power problems. Also I've hooked it up to my house wiring, so the Vonage box powers all the phone jacks.
Only an occasional fax problem, usually it's been fine. And my Tivo can make its daily call too.
I have the $34.99 personal unlimited plan. Saved me a ton of $$, and the only additional charges are 3% FET and $1.50 for 911 and other things they need to pay local telcos for.
Total of $37.54 per month. A far cry from the $58.80 I was paying Verizon without even a single long distance call.
Don't forget, there's a 14 day trial too. So if you don't like it for any reason, you can return the equipment and not even owe for the first month. There's also the referral program. If someone you know registers your email addy with them before you sign up, you both get a free month.
MarkB