How does Mobile MM use data for free?

Regarding free data for mobile MM. Everyone is looking forward to it, but who knows how 'Meimei' gets free data? With the same access point, why can 'Meimei' have free data, but QQ and UC cannot? It's really puzzling. I believe everyone has tried numerous methods. Could it be that 'Meimei' has an identification system? Otherwise, how would Mobile know whether we are connected through 'Meimei' or QQ? As a newbie, I hope a few experts can study this. Any mistakes, I hope you can point them out and critique them.