The invention relates to a network part and a method for generating billing data in a mobile communications system employing a wireless application protocol. The network part of the mobile communications system comprises: means for setting up a bi-directional wireless data transmission connection to a subscriber terminal; means for transmitting a service request sent by the subscriber terminal to a contents server providing the service; means for transmitting response data generated in the contents server on the basis of the service request to the subscriber terminal; identifying means for identifying transactions associated with the service from among the service requests and the response data on the basis of the identification of the Internet address of the service referred to in the service request and the response data; and billing means for generating billing data for the service using the transactions identified on the basis of the service's Internet address.