Every time I pass by a real estate sales company, I will receive promotional messages from them. How did they do it? How did they know my mobile phone number?

This is a service of network communication service provider, similar to advertising service. The real estate sales company cooperates with the network communication service company, and it is required to publicize the crowd within a certain range. Your mobile phone can let the operator know where you are. As long as you enter the advertising range, you will receive a text message. Similar to taking a train, when you pass through a province or city, you will often receive welcome messages and some SMS advertisements from the local area.