IMS networks and methods are disclosed for charging for operator-assisted sessions. To perform the charging, an operator assistance application server (AS) acts as an interface between an operator system (legacy or IMS) and charging systems for the IMS network. When an operator-assisted session is initiated in the IMS network, the operator assistance AS receives a session initiation message in SIP, and transmits the session initiation message to the operator system to allow the operator system to collect charging information from an end user. The operator assistance AS then receives a service request message from the operator system that includes the collected charging information, and detects a charging event. The operator assistance AS generates a Diameter charging request message, maps the charging information from the service request message to the Diameter charging request message, and transmits the Diameter charging request message to a charging system to charge for the operator-assisted session.