voip proggy

[SEmerson]

What would be a good voip program to use. I live in the states but travel to costa rica alot. I would like to have free computer to computer calls. Also use the voip funtion built in wm6. I would also like to be able to buy time to call computer to land lines and have a incoming Phone #

Thanks

[OMJ]

tried skype?

http://www.skype.com/download/skype/.../download.html

I've used it only a couple times, seemed to work good.