I got sick of high prices and poor service, and switched to Vonage.  The sound quality is  not always great, but it seems to be improving.  I love just about everything else about Vonage.  It's cheap, I'm not paying money to the big companies, I can make unlimited local and long distance calling (please note: I don't generally call outside the US -- I know you can make out of country calls to some countries, but you should check it out and make sure you can make the calls you need).

It's also got lots of features for free that you'd pay more for with the big phone companies -- call waiting,...