Abstract: The present invention proposes a method for billing a subscriber (A, B) for data transmission in a communication network (NW; AN, CN) said communication network comprising at least one call control entity (CSCF) for controlling calls to be established from a subscriber (A, B) to a communication destination (B, A), said method comprising the steps of: forwarding a signaling message from said subscriber (A) to said destination (B), said signaling message comprising a message header and a message body, said message header including information descriptive for a content carried in the message body, analyzing said signaling message header at said call control entity (CSCF), and generating billing information based on the result of analysis.