Ad–hoc networks are becoming more and more successful in the marketplace as indicated by the increasing usage of Bluetooth and W-LAN networks. Despite all the successes so far and the promising future of ad–hoc networks, Internet connectivity will still be very important, and could quite likely be supported by cellular networks like GSM/GPRS or UMTS. Another possibility is to use ad-hoc networks as an extension of the cellular air-interface, leading to improvements in cellular capacity and coverage.The integration of WLAN and cellular systems has thus become the new focus of academic and industrial research, and standardization organizations such as the Third Generation Partnership Project (3GPP), which is mainly following the Universal Mobile Telecommunications System (UMTS) development, have started to carry out feasibility studies for this integrated network. The integration of cellular mobile and WLAN systems should be viewed and investigated from several perspectives. The main Challenge would be the architecture of the integrated network that could include both cellular system components and WLAN elements.