To provide a system for selling a management relay station automatic connecting device capable of being commonly used among cellular radio telephone sets and being detachably attached on them, in a communication service using VOIP (voice over IP) or Web by a communication charge prepayment system.

A management relay station device to which cellular telephone sets are connected via the Internet is provided with an available time registering means for registering a predetermined available time corresponding to the sales amount of the management relay station automatic connecting device which is sold in a database, in response to a sales registering request from a selling terminal device; and an available time adding means for adding a predetermined added available time corresponding to the the sales amount of communication services of the management relay station automatic connecting device which is sold to the available time which is registered in the database.