for now my favourite is Skype, it's a computer program:) wich gives us a power to call abroad to a normal land line or to another computer, and in Poland it's better then others because it's easy to pay for it and the connection is very good, you can also call inside Poland and it will be cheaper as well.
I mean easy if you have a polish bank account, you can pay over the internet and your Skype account is instantly charged with money. So to call using skype you will need a computer, internet and skype account:) the prices for international calls are super low.
the link:
www.skype.com or a polish one :
www.skype.onet.pl
