A great majority of the EU citizens already owns a cellular phone. An increasing part of these phones are smartphones with a broadband internet connection. This growing network of smart internet enabled devices could act as a dense sensing network, as well as a tool for individual informing and tasking of mobile citizens and volunteers.In order to fully harvest this new resource, we need to understand its rules and develop adequate tools. This paper lists some of the peculiarities of ad-hoc volunteer networks supported by smartphones. It furthermore compares the capabilities and limitations of these networks with other means of observation gathering and activity coordination. This includes: (1) a reflection on the motivation for users participation; (2) human and technical limitations of smartphone-enabled volunteer networks; (3) legal and ethical challenges; (4) reliability and usability issues; as well as (5) issues related to trust and quality of information.The second part of the paper presents our experiences with design and prototypic development of the tools supporting volunteer efforts in the field of environmental monitoring, e-health and crisis management. This development is presented in a wider scope of the “Future Internet Public Private Partnership” research programme.Finally, the paper summarizes our findings and recommendations for further developments.