yahoo messenger

I don't think it is free. You will be charge for that but in the lower rate than make international call via wired or unwired phone. Actuall it used same technologies but the medium is using internet. Well to use that you need microphone and internet connection. For pc to pc call, i suggest you used skype. Here for your reference about skype. It's free for real, not like YM. www.skype.com/download

i beleive you can chat through voice using yahoo messanger as it is offered all you do is use a microphone with it