Communication networks and associated methods are disclosed that provide offline charging in IMS networks. One of the methods includes receiving call signaling for a call from an access network serving user equipment for the call. The call signaling includes an access network identifier for the access network. The method further includes identifying location information related to the access network identifier. The method further includes determining a local time for the user equipment based on the location information. The method further includes generating a charging message for the call, and inserting a timestamp in the charging message based on the local time for the user equipment. The timestamp in the charging message provides the billing system with the local time for the user equipment to allow for variable-rate billing.