Complementary characteristics of the WLAN and WWAN networks have led to the current research efforts towards their integration. The integration can be done at different levels in the network, resulting in interworking architectures of different capabilities and with different degrees of complexity. We concentrate here on the WLAN integration at the UMTS radio access level. Due to diversity of the existing as well emerging higher-capacity WLAN technologies, their gradual integration into the future integrated mobile network, while keeping the operators? investments protected, becomes an important issue. In this paper, we address such an interworking architecture and discuss necessary modifications, aiming at defining a framework that would require as minimal modifications as possible for any new type of the WLAN technology that is to be embedded.