A device and a method of subdividing data service charge in mobile communication network is disclosed. In one embodiment, the method includes receiving a billing initiation request signal from a wireless data service device (either an interworking function (IWF) unit or a packet data serving node (PDSN)), producing a usage-amount data for the subscriber based on at least one of the type and amount of data being transmitted through the wireless data service device on the mobile communication network. The method also includes, responsive to a billing end request signal, received from the wireless data service device, transferring a billing request signal, requesting to bill the subscriber for the usage-amount data, to an authentication, authorization and accounting (AAA) unit. In one embodiment, the above method can apply to a graduated billing for the each service group in the mobile communication network.