Am I right that if I use my iPhone (which I have not yet bought) to make a WhatsApp to WhatsApp call then the position is as follows?
If I am using wifi, this activity does not incur charges (because whatever is done through wifi does not count as either "data" or "minutes"?), but
if I am using the cellphone network, this activity will count under "mobile data" or "data allowance" (or perhaps "minutes"?), and therefore it will incur charges, being paid for out of either "data" or "minutes" or perhaps both?
Please assume that I have a PAYG arrangement that allows a specified amount of "data" and number of "minutes".
I have not used a smartphone before, and although I have read a few pages the exact meaning of "data" and "minutes" as these terms are currently used remains somewhat opaque to me. Thus "minutes" seems to refer only to voice calls placed to a phone number through the cellphone network. But if the call is made from WhatsApp to WhatsApp then it is still a voice call (and also a video call) made to a phone number, even it obviously goes through the internet (and requires a continuing transfer of digital data). As for the actual connection required for a WhatsApp call, it may be made through wifi or it may be made through the cellphone network. If it goes through the cellphone network, does that make it count as "data" rather than "minutes". As I understand it, even a short video can amount to a lot of data.
Where is it documented what is considered data on iPhone for cellular carriers?