Call7

http://www.galaxytabusers.com/galaxy-tab-tips/how-to-use-galaxy-tab-as-a-phone-free-incoming-and-outgoing-calls/

Check this article for step by step instructions on how to make free phone calls from your Samsung galaxy tablet or any other android phone or adroid tablet.

It does not require any hack and you will be able to make phone calls to any number in USA and Canada for FREE.