using dummy phones is only have sense if you do not want to be tracked by GPS or some app ( criminals use such phones very often ).
It's a bit of a fake sense of 'security' to be honest. Governments can pretty easily track 'dummy' phones by following their carrier signal and from there extract any sort of data holding importance to them, or even censor communication.
It is not perfect way to remain undetected, but it is much harder to discover someone who use mobile phone without GPS. However there are ways to stay under radar if you need, just use
burner phone.
I think even people in some 3rd world countries have the possibility to use smart phones these days because they are become pretty cheap. If you just look how much cheap smart phones is produced in China it's not hard to imagine that all world users will have such phones in some 5-10 years or even before.
I agree with you. Many cheap smartphone models have already appeared in the markets. Even the non-rich people can buy them now. Of course, I'm not talking about the new iPhone, Samsung Galaxy or other premium-class smartphones.
Undoubtedly, the quantity of ordinary cell phones will be decreased in the future, therefore mobile applications which support making transactions of Bitcoin or other crypto currencies will be in demand.
I think that the global mobile payment market will indeed reach $4.6 trillion by 2023, because customers like such convenient methods for buying goods and services.
You can buy smart phone for some 50$ or even lower price, this will not be top brand as you say - but I have one which is work for 5+ years without problem and it cost me 20% of some top model phone at that time. Industry of mobile phones is so strong in China, almost every day they launch some new model. You can get Ulefone Power 5 for some 250$, and it have 13000 mAh battery (strongest in the world) + excellent specifications.
Number of users who use smart phones in 2018 is estimated to 2,50 billion users and it will be around 3 billion by 2020. No wonder that China is the leading country in the world by number of smart phone users, by 2020 half of their population will use smart phones.