Spanish and french users, I need your help about choosing a mobile operator. (ROW gib inside)

Hello! First of all, thank you all for any help, because this is somewhat important.

Will someone from Spain or France (preferably Spain) tell me about the mobile operators there. I'm looking for a prepaid plan with 0 euro monthly fees and cheap calls to eastern Europe (specifically my country - Bulgaria).
Another thing I'm interested is the fees that apply when you use your phone outside the country you got the plan from. ( for example if you got the plan from Spain, what fees will apply if you go to, let's say, Belgium and call to Bulgaria from there)

I've tried to research this from here, but I can't speak spanish or french and most of the operators sites don't have an english version.
If you're wondering why I'm asking this, my father is working in Spain and when he calls home from his bulgarian card, the prices are unbearable.

Thanks again, have a gib as a token of my gratitude.