Calling Card to 250 countries.

Hi,

Ive recently been researching the whole calling card business,
and from what i understand, you need equipment and lines at one end in a country (australia for example) and equipment at the receiving end (india for example) to be able to make a call..

Ive seen very little and small calling card operators provide service to over 250 countries..
Surely they dont own equipment in 250 countries??! Is there some kind of service in which they ‘route’ through or something?? im a bit hazy on this..

I know for sure they dont have all this infrastructure in 250 countries, but could be using someone else’s services and branding it as their own.. Is there any company like that out threre? Im in australia..