Techniques for allowing access based online charging in cases of multiple user agents (multi-UAs) scenarios where the instances are registered to different telephony application servers (TASs) are discussed herein. For example, a user device may support a native number and multiple virtual numbers linked via a user account. When servicing a call, the user device may determine a served number to service the call from. If the served number is not the native number but a virtual number, the native-line server may handle the call session, but the online charging session will be handled by the virtual-line server. The native-line server may use session initiation protocol (SIP) information to send updated information for charging parameters to the virtual-line server, including network access transfer for accuracy in online charging logic.