Although the widespread deployment of cellular networks guarantees mobility in large ranges, it cannot completely support multimedia data. Similarly, although the explosive growth of WLANs provides the convenience of wireless with high bandwidth, it lacks large range support. Thus, in this paper, we propose a new approach, ABC2, for seamless mobility such that our approach provides both high bandwidth and large ranges. ABC2 will provide not only an "Always Best Connected" but also an "Always Best Complemented" interworking architecture between cellular networks and WLANs. ABC2 architecture is novel in that packet data network is layered on top of circuit switch network such that it can use current legacy telephone networks for mobility management and provide multimedia data with low cost investment as the Internet advances to the higher bandwidth. In our analysis, we show that ABC2 performs better in terms of location updates, handoff latency, and signaling delay compared to most mobility protocols dependent on Mobile IP.