Most research on mobile ad hoc networks assumes a medium access (MAC) protocol similar to 802.11. Nevertheless, such networks can be built on top of any medium access scheme. An example are Bluetooth multi-hop networks (so called Scatternets). In practice, many devices support several interfaces although the protocol stack used in each interface tends to be interface specific at the lower layers. This limits the ability of a device to switch back and forth between networks as need and opportunity dictates. As a step towards providing a more flexible handover infrastructure, in this paper we address the issue of integrating heterogeneous, mobile ad-hoc networks that use different MAC layer protocols. The goal is to provide an end-to-end communication abstraction that hides heterogeneity. In the paper, we discuss different possible designs with regard to application transparency, performance and mobility. Using these ideas, we describe an IP based heterogeneous mobile ad hoc testbed using Bluetooth and IEEE 802.11 that implements a virtual interface approach as the end-to-end abstraction. Furthermore, we also provide a detailed evaluation of the system in terms of throughput and handovertime.