A sender of a message uses a sender's portable telephone device to register, by way of a communication network, to a service agent: user's information, communication partner information, sending conditions, and a message. The service agent monitors whether the sending conditions are met, and when the sending conditions have been satisfied, executes processing to send the entered message to the receiver's portable telephone device of the communication partner that has been registered. The sending conditions include conditions relating to presence information that the communication partner can always access by way of a communication network through the communication partner's own communication terminal.