It has been emphasized that students and teachers have dissimilar ideas about how mobile phone use could be utilized and limited. Moreover, these differences have been identified as a crucial problem that has caused conflicts in education. In order to resolve the problem, research has stressed that it is very important to increase teachers' knowledge about how mobile phones can be used in students' work. However, the topic of how teachers could increase their understanding related to students' ideas has remained largely unexamined. Thus, this pilot study explores the following research questions using cultural-historical activity theory and qualitative methods: How is teachers' "possibility knowledge" influenced when they are exposed to students' ideas about how mobile phones could be both supportive and problematic in school activities? What are the similarities and differences between the students' ideas that have, and have not, influenced the teachers' possibility knowledge of mobile phone use? The results show how the teachers' possibility knowledge increases concerning the features that could be both supportive and problematic and must be limited by rules and a division of labor. Moreover, it transpires that the teachers' possibility knowledge is not always affected. It appears that the teachers' understanding is influenced if they can relate the students' ideas to the teachers' division of labor. These results could be used by schools to resolve problems caused by the different ideas of students and teachers regarding mobile phone use. The results could also be used when implementing mobile phones in educational research.