The smartphone, through its small size, ease of use, proliferation of free or cheap apps, and constant connectivity, changes our life in a way that goes well beyond what we experienced with previous media. This study examined smartphone users' perception and evaluation of their dependent behavior during the 2014 communication blackout (March 20) that lasted 6 h in South Korea. Based on the interviews with 70 smartphone users between March 22 and March 30, 2014, this study identified two types of dependence – functional dependence which stresses instrumental usefulness of the smartphone and existential dependence which focuses on obsessed, often unconscious, attachment to the smartphone. Although the two types of dependence may overlap each other, those who perceive existential dependence were more reluctant in acknowledging negative aspects of smartphone use than those who perceive functional dependence. In addition, functionally dependent users were more willing to change their dependent behaviors than existentially dependent people. Smartphone users, regardless of their types of dependence, denied that they were addicted to the smartphone. •There are functional and existential dependence of smartphone heavy use.•Functional dependence stresses instrumental usefulness of the smartphone.•Existential dependence focuses on obsessive, often unconscious, attachment.•Existential dependent users are more reluctant in acknowledging negative effects.•Functionally dependent users are more willing to change heavy reliance on the smartphone.