I just researched what "kbisiar" is refering to and it seems legit. You need a VoIP app for your phone and that's about it.
Check out these links:
http://techtips.salon.com/use-wifi-i...calls-306.html
https://itunes.apple.com/us/app/ical...293837001?mt=8
http://www.appbrain.com/app/icall%3A....icall.android
