Is short message cat legal?

Illegal. Short message cats are prohibited by the state and belong to illegal communication equipment. Once found, but should be investigated for legal responsibility. A short message cat is actually a device used to send and receive short messages. Just like the mobile phone we use, we need the support of the SIM card. When sending and receiving short messages, insert a mobile phone card that we usually use in the short message cat, plug in the power supply, and connect with the computer through the data cable (USB or serial port or network port), so that the function of sending and receiving short messages can be realized in the application management software of the computer.