Usually when you see the 'FREE PHONE CALLS' ads it means free calls between people who use the software and then you pay to call from the service to a landline at much cheaper rates than a phone company.
Well for awhile now Gmail actually has a phone call feature in it that enables you to call from within your browser to any landline, anywhere, for free. It works great with any headset and is ridiculously easy to set up.
To access the feature signup/login to a Gmail email account and look on the left hand side of the screen towards the bottom, you'll see a little phone icon. Click on this icon and your dialpad will pop up on the bottom right where you simply type in the number and press dial.
Its unknown when they will start charging for this service but for now take advantage!