Deployment of IP multimedia services with guaranteed Quality of Service (QoS) is a primary requirement for Beyond 3G (B3G) systems. In this paper we propose a new architecture to support Internet QoS-sensitive services (e.g., video-conferencing, voice over IP, interactive gaming), thus providing users with end-to-end QoS guarantees. In particular, the paper discloses a new hybrid Intserv/Diffserv scheme for handling IP packets and an interworking procedure with the RSVP protocol which allows to support QoS over an integrated, multi-segment network. Such scheme is implemented by means of a suitable Quality of service Support Module (QASM). Advantages and drawbacks of QASM are discussed and the impact on both system architecture and Multi-Mode Mobile Terminal is investigated. Performance evaluations, carried out via computer simulations, confirm the effectiveness of the proposed solution.