With Apple focusing on creating new mainstream users (beginners) using their devices, there are likely far more users making calls with iPhone than not.

With how much MacBooks have increased their phoning home.. But having visibility, wish I could say the same for iPhone/iPad as easily.

Your point about spam calls is a good one. I'm not sure how many years you've had your number, or how many people had it before you. I have had my current mobile number a long time and the spam calls from me being on a list are minimal, minus voip robo-dialers. Spam callers seem to use easily changeable voip numbers (sometimes calling from similar voip numbers to my own), part of the spam call issue is likely to encourage the voip phone providers to pay attention to high usage/turnover numbers.