A short message sending tool similar to a mobile phone will automatically find people nearby.

You are talking about a pseudo base station, which is an illegal product. If you use it to send text messages, you will go to prison for at least three years. It is best not to touch it. It costs at least tens of thousands of dollars to buy such equipment, which is not cost-effective. If you want to use SMS group to develop business, I recommend you to use onesmser SMS platform, which is a third-party SMS service provider with good reputation in the industry.