Is it illegal for SMS group sending service providers to provide telephone numbers to customers?

to a certain extent, this will involve breaking the law. You send short messages in groups. Your duty is to send regular short messages to the enterprises you cooperate with, not to provide them with numbers. The numbers are provided by enterprises or businesses, and they have accumulated them themselves. Why did you provide them? Is there any doubt about this? You should consult a lawyer, and everything will go wrong as soon as there is a problem.