Skype uses P2P technology to connect you to other users.   You can make  perfect quality free phone calls to your friends all over the world just simply using your computers sound card, speakers and microphone.

Features:

• Unlimited free high-quality worldwide voice communications
• Superior sound quality
• Works with all firewall, NAT and routers
• Friends list shows you when your Skype friends are online and ready to talk or chat
• Your calls are encrypted end-to-end for superior privacy
• Based on cutting edge P2P technology

Changelog:

• change: Internet Explorer plug-in updated to version 2.2.0.147
• change: Audio device checking before placing a call and changing to windows default if previous device is non existent
• change: Re-enabled config.xml keys for higher resolution and frame rate video
• bugfix: Skype generated high amount of page faults
• bugfix: Skype crashed when unknown PSTN number was added to conference call
• bugfix: Skype crashed on occasionally when computer was locked
• bugfix: Skype crashed infrequently on shutdown
• bugfix: Contact search window was incorrectly drawn when there were zero results
• Localizations updated

Download: Skype 3.6.0.244