Returning to my lack of understanding and consternation and desire for elucidation vis-à-vis the costing of smartphone use:

I have asked friends and relatives about their use of such, and nary a one can explain the charges. This from people who would ordinarily comparison shop to save a couple of shekels on any given item. I must conclude that they are numbskulls when it comes to their communication needs.

Apparently whatever "data" is, it is measured in GB. Can anybody give me a sense of how one might calculate the various types of cellphone uses in terms of GB? By that I mean how many phone calls make up a GB? And how many/much of other things make up a GB? I have absolutely no sense or comprehension of how one might determine potential usage.
Everything I see tells me that service providers (eg, telecoms) are purely and simply fraud artists trying to scam people for as much as they can.