Why don't they just buy it from Google and Facebook, like everybody else?
I normally never give out my mobile number. But I did give it to a .gov.uk health information website when I was asking urgently about Covid. The site promised anonymity of all my data, but a few days later the junk calls on my mobile upped by an order of magnitude. Health services feature strongly, when I can understand the foreign accents.
Mass surveillance systems? Why bother?