In two days at the beginning of October, five million Chinese registered for 5G. Most or all will soon be activated. I have confirming data points. By the end of 2019, I’m confident at least 12M will sign up and more likely 20M or so.
50M will be reached in the first half of 2019, as phone prices drop to under US$300. Most Chinese estimates for 2020 are 150-200M, far more than the rest of the world combined.
The highest estimate I know in the West for worldwide 5G in 2020 is 160M; most are lower. I’m about to stick my neck out and go with the Chinese estimates. The only caveat is production limits at TSMC, which manufactures most of the chips for 5G phones.