I often see the term"typical two call system".  What is that?

Two Call System -- The general location is revealed during the first call; location specifics are revealed on the second call.


Taken straight from the "Definitions, Acronyms, Abbreviations, and Terms" post; see link below.

But I'm still not clear. Is this for in-calls only? Is the first call giving you directions to be in a certain neighborhood then the second one gives you the complete address (or maybe directions from there?). Is a cell phone pretty much essential for this? Thanks in advance for the answers.