thanks for precisons.
And does it seem good if:
I m france with my prepaid orange for example and him with united mobile.
He calls me and i can see on my phone that it's him (with number appearing)
So i can call him back with my orange phone.
So i can identify that's it's time to call him
and i'm able to recharge in france with orange sratch cards.
Do you confirm if he would pay 0 if i'm doing it?