This study examined the effect of and relationship between self- and prototypical identity influences on high-level mobile phone use from a theory of planned behavior (TPB) perspective. Participants were 252 university students who completed 2 questionnaires, 1 week apart. The first questionnaire assessed the standard TPB constructs (attitude, subjective norm, perceived behavioral control), as well as self- and prototypical identity influences. The second questionnaire assessed level of mobile phone use in the previous week. Support was found for the TPB in predicting high-level mobile use intentions and behavior. Self-identity and prototype similarity, but not prototype favorability, also significantly predicted intentions. The effects of prototype similarity on intentions were mediated via self-identity processes.