Ekiga is a Voice over IP client available for both Linux and Windows.
Register at http://www.ekiga.net. You get a SIP ID as sip:email@example.com with a numeric alias.
Download Ekiga, Opal and pwlib from the Fedora 7 website.
Set up your microphone:
Choose OSS device. Change to add MicBoost, Mic1, Capture. Change device to ALSA.
Set up Mic volumes read and gree to be ON.
Start ekiga as $ nrtsdsp -m ekiga and setup preferences.
Call other people using
To dial US toll free numbers, call *013- like this *013180011200121
Test your phone with firstname.lastname@example.org