I've thought about this a lot, too. Here are my ideas:
- Set up an asterisk box (make sure it has chan_celliax installed, for Skype)
- Purchase unlimited US SkypeOut ($30/year)
- Purchase an unlimited local DID from les.net for $3.99/month, or if your faves list isn't limited to just your area code, sign up for an ipkall number (free)
- Set up asterisk so when you call your DID, it lets you enter in a PIN and a phone number and dials out via Skype
A bit of work for (almost) free calls...