When interworking two or more networks, such as a wireless local access network (WLAN) and a mobile communication network, user billing and service charging should be accurately collected and processed. To do so, certain types of service usage and charging information for certain users can be deleted depending upon the type of service provided to the user. Also, service usage and charging information can be periodically collected depending upon the type of service being provided. Furthermore, WLAN wireless access service usage and charging information, as well as mobile communication network service charging information can be collected upon correlation therebetween.