A Proof-of-concept RCT of Version 3.0 of the Smoking Cessation Smartphone App "Smiling Instead of Smoking" (SiS)

This is a nation-wide proof-of-concept randomized controlled trial conducted entirely remotely. Participation will last 6 months and entails: * Completing a scripted onboarding call (approximately 30-45 minutes) * Making a quit attempt * Engaging with smoking cessation support (randomized) over the course of seven weeks, one week prior and 6 weeks following the originally chosen quit day * Completing five online, REDCap-administered surveys, administered prior to the quit day (online, as part of a screening test), and at 2-week, 6-week, 3-month, and 6-month follow-ups of the participant's chosen quit day The Aims of the study are: 1. Test for differences between randomized groups on the primary outcome (i.e., self-efficacy to remain abstinent, as measured via the Smoking Self-Efficacy Questionnaire), as measured at end of treatment (i.e., 6 weeks after the participants' chosen smoking quit day) 2. Test for differences between randomized groups on secondary outcomes (as listed in Detailed Protocol) 3. (exploratory) To test, via mediational modeling, how treatment via the proposed app conferred benefit; or, if not effective, if failure is due to the treatment failing to impact hypothesized mechanisms of change, or because these mechanisms fail to impact outcome.