What is the reason why unicode mobile phone number can't be changed to digital number when SIM800C sends SMS?

SIM800A is a mobile phone communication module based on GSM, which can send short messages and make phone calls. You can send a recent project and use its SMS function to record the debugging process.

SIM800A adopts serial communication and can be operated by sending AT command. Therefore, firstly, the AT command is sent manually by the serial debugging assistant. Debugging instructions of AT instruction (turn)

I use USB to serial port connection module to communicate with the computer. The USB-to-serial module has its own 5v output, so I used it as the power supply of SIM800A module at first, but I found that I always returned an error when sending some inquiry AT commands. Later, I consulted the debugging manual provided by the merchant, which mentioned a method to check whether the module works normally, that is, calling the module. If you are prompted to turn it off, the module will not work properly. I tried, and sure enough, I was prompted to close it. Then there must be something wrong with the hardware connection, and I noticed that the manual emphasized the importance of power supply, so I doubt the power supply ability of USB to the serial module. Connect the SIM800A to an external power supply, so that the computer and USB serial port module only need to connect three wires (TX, RX, Gnd), and then call the module, without prompting to turn it off, indicating that the module works normally and the problem is solved.