In a caller information notifier system, a calling terminal transmits a calling signal having a phone number for callback inserted which is different from the phone number of the calling terminal. When a callback is tried from a called terminal, a communication network server, where the calling signal passes, determines the relationship between the phone number of the calling terminal and the phone number for callback inserted in the calling signal to authenticate the phone number for callback. A terminal which receives the calling signal extracts the phone number for callback from the calling signal and keeps the extracted number as a callback phone number. The callback phone number is, for instance, an FMC service number. The probability of success in reaching a caller is thereby increased.