Integration of Carrier Wi-Fi and 3rd. generation partnership project (3GPP) networks is currently one of the hottest topics in the agenda of the mobile industry. Wi-Fi is one key element of heterogeneous networks to handle the traffic explosion in the coming years and as such an integral part of a complete mobile broadband solution. In order to exploit its full potential, Wi-Fi will more and more be seen as an additional radio access technology (RAT) in the mobile network. A path to this is currently being paved in different 3GPP and Wi-Fi related fora and accomplishing this vision requires a number of elements to be considered including strategies for access selection and a common network management framework. This paper addresses a contribution towards this direction. We demonstrate a common performance monitoring (PM) system for Wi-Fi and 3GPP networks. The solution relies on the correlation of performance traces from both technologies and Wi-Fi access point (AP) probes. Interworking key performance indicators (KPIs) are defined assuming the state of the art for Wi-Fi and 3GPP seamless authentication, based on the extensive authentication protocol-subscriber identity module (EAP-SIM) framework. The demo consists of giving an overview of the system architecture, description of different mobility use cases for vertical handovers between Wi-Fi and 3GPP networks and the presentation of the interworking performance recorded from active tests.