The convergence of mobile and computing technologies have revolutionized the current technology and human interaction environments through the use of portable devices that offer the possibility to access information and communication services in a ubiquitous and mobile fashion. This paper describes four characteristics of mobile devices which play an important role in supporting learning activities: personal proximity, mobility, connectivity and spontaneity. We present a brief analysis of the main components of the educational process supported by mobile devices pointing out some challenges and opportunities of using mobile devices to support learning in educational contexts. We are particularly interested in the interactivity and usability aspects involved in the engagement of students in educational tasks using smartphones in conjunction with mobile collaborative servers.