Skype is an internet telephony program that uses VoIP (Voice over IP) protocol.
This sound quality of this protocol is amazing and it is being developed by Global IP Sound almost all companies use it for their VoIP phones.
One example is Cisco systems (World leading networking company): Cisco VoIP Phones
Skype uses VoIP and it supports NAT (Network Address Translation) protocol which means that if you're behind router (local network) it will work flawlessly.
You can phone anywhere you want absolutely for free there's absolutely no charge or whatsoever (only your fixed internet bill).
You can Download Skype here:
http://www.skype.net/products/skype/windows/?autoload=true
Here are some Professional Audio extras i made for Skype (You must have those):
Cisco Ringtone (same as the cisco VoIP phones ring)
New Message Audio Efect
New Mail Audio Efect
