In multi-hop wireless networks, data packets are relayed in several wireless hops from their source to their destination. Based on whether a fixed infrastructure is used or not, we can distinguish two types of multi-hop wireless networks: pure ad hoc and multi-hop cellular networks. Pure ad hoc networks do not rely on any fixed infrastructure; hence, the packet relaying service has to be provided solely by the end user devices. Multi-hop cellular networks rely on a set of base stations that are connected to a high speed backbone network; here, data packets have to be relayed by end user devices from the source to the backbone and from the backbone to the destination. Multi-hop cellular networks are a potential evolution of both voice-centric networks such as GSM and data-centric networks such as CDPD or IEEE 802.11... In this paper, we present our ongoing work on the design of mechanisms that stimulate collaboration of end users in both pure ad hoc and multi-hop cellular networks. We put the emphasis on stimulating packet forwarding, as this is one of the most fundamental services that end users should provide to each other.