This study examined mobile phone use in the classroom by using an experimental design to study how message content (related or unrelated to class lecture) and message creation (responding to or creating a message) impact student learning. Participants in eight experimental groups and a control group watched a video lecture, took notes, and completed tests of student learning. The control and relevant message groups earned a 10-17% higher letter grade, scored 70% higher on recalling information, and scored 50% higher on note-taking than students who composed tweets or responded to irrelevant messages. Sending/receiving messages unrelated to class content negatively impacted learning and note-taking, while related messages did not appear to have a significant negative impact.