bloodbruise

I recently unlocked my Samsung Captivate Galaxy S. I currently live in Mexico, but all my family is in the states. My goal is to get Google Voice to work over wifi networks, and NOT my carriers number. As of right now Google Voice says "cant complete call" every time i try to make a call via Google Voice. The Sim im using is a regular sim but for Mexico, so im having some issues. I herd you can use Google Voice via SIP, is that true? Anyone have any ideas of maybe even apps i can use that will allow me to get incoming and send outgoing calls via Google voice over wifi?

BTW sorry if this isnt the right area to post, this is my first post anyway...