A system for billing Internet protocol (IP) telephony, or other telecommunication calls transmitted over data packet networks, is provided. Calls may be routed over networks of different types, e.g., H.323 networks or IP voice networks. Different types of network devices, e.g., call managers, switches, or gateways, may transmit legs within a call. Each device type typically generates call records that have data fields unique to that device. In order to generate a single billing record for each call, call records are standardized and then matched with call records from other devices. Key fields within call records that may be matched include: call connect timestamps, signal start timestamps, calling party identifiers, called party identifiers, or network device identifiers. Timestamps within call records may be synchronized from a common time server.