I found this site and thought I'd share it.
Go there and click on the "Best Rate Calculator". Then you enter the first 6 digits of your phone # (area code and prefix). Next, enter the number of hours you talk each month state to state, then how many minutes in-state. The search engine will find the best rate from about 15 different options like Qwest, etc.
I signed up with a rate of 4.9 cents state to state!