Abstract: The present invention is intended to provide a call system which can authenticate a call initiation request from a proxy dial server apparatus with a caller number specified by the proxy dial server apparatus without adding special processing. In the configuration according to the present invention, proxy dial server apparatus first requests telephone server apparatus to call a telephone number of a user. In this event, proxy dial server apparatus uses the telephone number of the user as a caller ID. Upon receipt of a call request, telephone server apparatus transmits an authentication challenge to proxy dial server apparatus for authenticating the caller ID. Upon receipt of the authentication challenge, proxy dial server apparatus generates a response using a user ID and a password previously registered in association with the user's telephone. This results in successful authentication by telephone server apparatus, allowing a call to terminate at the user's telephone number.