This paper is concerned with the issue of students\' use of mobile phones in a classroom and at school, as many school teachers argue that the behavior is one of the main causes to distract students from attending class activities. We investigated a case of middle school, located at Seoul, where an ad-hoc school policy has been set to prohibit students to bring and use mobile phones at school. How did students respond to the policy? And what changes have been brought to the students as a result of the policy? To answer these questions, we analyzed survey data earned from 807 students as well as narrative data from a focus-group interview. The findings of the study are as follows: (1) 88.5% of the respondent students were against the policy due to the inconveniences of communication, (2) 64.4% of the students, however, agreed that the use of mobile phones should be prohibited during a class, (3) yet, the majority of the students seemed not perceive positive changes in class atmosphere or in school life, (4) new patterns of play culture emerged such as using MP3 or other electronic game devices, and playing a soccer. Along with the findings, this study suggests two critical factors that can lead the policy being successful; teachers\' consistent guidance and alternative communication media or facility that can be readily accessible by the students