This paper presents a study addressed to evaluate the variation in perceived QoS experienced by a user running multimedia applications in a heterogeneous wireless network. To perform this evaluation, a real-time testbed emulating an all-IP B3G network that includes UMTS Terrestrial Radio Access Network (UTRAN), GSM/EDGE Radio Access Network (GERAN), and Wireless Local Area Network (WLAN); and the corresponding common core network (CN) based on DiffServ technology and Multiprotocol Label Switching (MPLS) has been used. Results for videostreaming and video conference applications when running under interruptions due to a vertical handover (VHO) are included in this paper, pointing out the variations in behaviour of different applications.