This paper aims at presenting two case studies, with use of cell phones in Calculus I classes, in the first semester of 2011, at a federal institution. Devices belonged to the students, to identify, in real context, advantages and difficulties of such use. Methodology was based on guidelines set by M-learnMat, a pedagogical model to guide m-learning (mobile learning) activities in Mathematics. It was developed by the authors of this paper, based on Activity Theory, and focus on Higher Education. This paper begins by providing an overview of the Activity Theory, and presenting the M-learnMat. This is followed by descriptions of the application of the model, specifying the resources for cell phones used and methodological procedures adopted. The article closes with considerations on the experiment, describing advantages and difficulties of using cell phones. Despite the difficulties, the experience was positive.