  The coupling of scale-free networks with mobile unstructured networks is
certainly unusual. In mobile networks, connections active at a given instant
are constrained by the geographical distribution of mobile nodes, and by the
limited signal strength of the wireless technology employed to build the ad-hoc
overlay. This is in contrast with the presence of hubs, typical of scale-free
nets. However, opportunistic (mobile) networks possess the distinctive feature
to be delay tolerant; mobile nodes implement a store, carry and forward
strategy that permits to disseminate data based on a multi-hop route, which is
built in time, when nodes encounter other ones while moving. In this paper, we
consider opportunistic networks as evolving graphs where links represent
contacts among nodes arising during a (non-instantaneous) time interval. We
discuss a strategy to control the way nodes manage contacts and build
"opportunistic overlays". Based on such an approach, interesting overlays can
be obtained, shaped following given desired topologies, such as scale-free
ones.
