Correct me if I'm wrong, but isn't there a monthly fee for Vonage? With Ooma, you can get a premiere account with added benefits, but for the basic service you only have to pay for the hardware and the service is completely free.

I could have sworn there was another reason I recommended Ooma over Vonage to my parents about 3 years ago, but I can't remember it at this point. I think the free thing was the basic reason. Basically it allowed my parents (now just my mom) to save an incredible amount on phone service. I think the cost of equipment was made up for about 18 months ago, so now my mom is getting great savings out of it.

And I definitely think the call quality is excellent - better than POTS.

*edit*
If anyone is considering moving from a POTS service, the international calling is ridiculous too. I had my mom put $10 in her Ooma calling "bank," and now she can call her friend in London for at least 9 hours without running out of money.