Thanks to Gerry McKiernan for pointing out a free e-book
Ally, M. (Ed) (2009) Mobile Learning: Transforming the Delivery of Education and Training. Athabasca Press. 978-1-897425-44-2 (e-book) (There is also a paperback, $39.95, ISBN 978-1-897425-43-5) It includes some overview chapters and also chapters focusing on specific studies and applications.
Photo by Sheila Webber: Bicycles at Leiden station, Netherlands, April 2009