Howdy Softphone 0.9b
This software plus any computer headset turns your computer into a phone.
The software can work under 98 percent of NAT routers/firewalls without any configuration at all. It offers support for over 100 computers on the same LAN. The software can divert calls to any other phone in the world, even if your computer is off. With international call divert, you can be away from your home, office or even out of the country, and you'll still be able to receive all calls.
The program is free to call other Howdy Softphone users, you must pay to call mobile and home phones.