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.