Taiwan has been the top country worldwide in terms of its adoption and use of mobile phones. This study explores the permanently online (PO) and permanently connected (PC) phenomenon in mobile phone use among Taiwanese university students. It seeks to determine whether attachment styles are a distinctive factor that influences PO and PC (POPC) behavior and leads to various levels of well-being. The results of this study provide initial evidence that Taiwanese users highly depend on their mobile phones for PC and PO activities but perceive that being permanently connected causes interpersonal stress. Although the findings showed that all styles were positively associated with PO, only the secure and anxious styles predicted PC. Regarding mobile phone activities, the avoidant attachment style was not associated with any activities, the secure attachment style was positively associated with online and voice communication as well as information-seeking activities, and the anxious attachment style was associated only with voice communication. Furthermore, attachment styles lead to various levels of interpersonal stress through PO and PC behavior. The anxious style interacts with PO on interpersonal stress. This study provides evidence that attachment style is a significant antecedent of POPC and its consequences in mobile phone usage.