Free access number for international calls?

Hi,
I moved into an apartment with a phone system that allows me to receive calls, but I cannot call out. Except to free numbers. I was told to buy international phone cards to call abroad, as they have free access numbers.

I was wondering if it is possible to sign up somewhere and get a fee access number after having bought credit from some company. Something like phone cards, except that you know the company and maybe get cheaper rates?
Thanks!