Is it possible for a prison to send messages by mobile phone?

Yes, it's just that different regions use different speeds. In some prisons in Tianjin, prisoners have been allowed to have a fixed number of short messages with their families every week, in order to help prisoners recover their emotions and reduce their psychological stress. However, there are not many prisons in China that allow this kind of contact at present, and it will be improved in the future.

Bring your cell phone in. Don't even think about it. It is the greatest pleasure not to let you reform through labor every day.