It means nothing without context. We need to see the passage in which you saw it.

It means taking big decision. Or we can say big opportunity .for example if I got selected for national team. It's big call for me

If I'm not wrong I think it means it's a big opportunity or a huge changes... If I'm not wrong

In my opinion, It means a very important call. Maybe, caller wants to announce a special thing !

If I'm not wrong I think it means it's a big opportunity or a huge changes... If I'm not wrong