What is the function of telecom quantum card?

Encrypt calls to prevent eavesdropping. According to China Telecom official website's information, when users use the quantum security SIM card specially made by China Telecom to make a call, they will combine the SIM card to generate a random key to encrypt the call content. If the caller also uses this customized mobile phone and quantum security SIM card, the received key will be decrypted. Because there is a key in the middle, others can't unlock it, so the conversation content is not afraid of being intercepted or monitored.