1. A call request processing system, comprising: a monitoring module that receives a call request from a calling party and generates a corresponding call alert message; a call alert module that receives and processes the call alert message; a keyboard; a signal receiving module electrically connected to the keyboard; a signal processing unit electrically connected to the call alert module and the signal receiving module; a signal reply module electrically connected to the signal processing unit; and an instruction setting module electrically connected to the signal processing unit and the signal reply module; wherein when the monitoring module receives the call request from the calling party, and the called party is communicating with another caller, the call alert module processes the call alert message to generate a corresponding alert information to inform a called party to respond to the call request from the calling party, the keyboard receives different key inputs to access and query corresponding operation instructions to represent a current call state of the called party, and the called party replies and informs the calling party the current call state of the called party according to the operation instructions; and wherein when the monitoring module receives the call request from the calling party, the keyboard receives corresponding key inputs to access and query corresponding operation instructions in a call state table built in a storage device to respond or call back to the calling party; and wherein the signal receiving module receives and transmits the key inputs, the signal processing unit carries out each key input of the called party in sequence, and receives the key inputs from the signal receiving module and accesses querying operation instructions corresponding to the key inputs in the call state table, the signal reply module receives the operation instruction from the signal processing unit and transmits the operation instruction to the calling party to reply and inform the calling party the current call state of the called party, and the instruction setting module receives the operation instruction and sets corresponding callback information comprising callback time, callback mode including vibration, message and ring tone according to the operation instruction.