Following the decline of investments in government extension services in the 1980s and 1990s, community- based extension approaches have become increasingly important. One such approach is farmer-to-farmer extension (F2FE), which is defined here as the provision of training by farmers to farmers, often through the creation of a structure of farmer-trainers. We use ‘farmer-trainer’ as a generic term, even though we recognise that different names (e.g. lead farmer, farmer-promoter, community knowledge worker) may imply different roles. 
Introduction
In the last few decades, information and communication technologies (ICTs) have provided immense opportunities for the social and economic development of rural people, and some technologies have surpassed others. Mobile telephony is one such technology that has developed significantly in the past few years, and the subscription rate in developing countries has gone up from 22 per 100 inhabitants in 2005 to 91.8 per 100 inhabitants in 2015. Mobile technology goes beyond geographic, socio-economic, and cultural barriers and this large increase in mobile subscriptions, along with the recent roll out of 3G and 4G technology, can play a big role in the development of rural people. Mobile phones are devices that can create, store, access, and share information anytime, anywhere. But they are more than that. When teamed with extension and advisory services, they can help improve the livelihoods of rural people by getting much needed timely information to their fingertips at potentially low cost. So-called mobile-based extension and advisory services (mExtension, see Box 1) enable value-added services, such as mobile agro-services and machine to machine services, (1)
which help farmers monitor their crops and farm machinery through mobile phones. While value-added services are generally fairly accessible to all the farmers in rural areas, machine-to-machine services are more cost intensive and require infrastructure that is often not present in developing countries.
