I've been using Vonage for the past 6 years. Sound quality is not an issue. i'm using TW Cable's regular Roadrunner package. My wife works from home and has a Vonage line for work and a Vonage FAX line in addition on the Vonage home phone line... so 3 lines. If you get Vonage you just need to go the user settings page and crank up the bandwidth for VoIP calls to the highest quality.
IIRC the TW Cable Phone service is like $35 plus taxes. Vonage is like $28 after taxes. It's cheap and decent service with lots of added features.
Vonage customer service can be so-so because, like so many others, they outsource to India. I've only had to call customer service maybe 3 times in 6 years and the last time a got an english speaking female who was not in India so maybe they've changed.