Use Gizmo Call to make free calls from your browser.

ChipChick.com:

“Gizmo Project is an excellent Skype alternative that works on both Mac, PC, and many cell phones. And now Gizmo Project has a new service called Gizmo Call that allows you to access your Gizmo Project account to send and receive phone calls, from any browser. All you need is a headset and you’re ready to go. They’re offering 5 free minutes of calling, or 10 free minutes a day if you register, however each call is capped at 3 minutes which can be a pain. Still, it’s hard to complain about something that is free. Aside from Gizmo Call, they’re also offering another neat web based service called Gizmo SMS for sending free text messages to almost any phone internationally.”