Text messaging has successfully supported smoking cessation. This study compares a mobile application with text messaging to support smoking cessation. Young adult smokers 18-30 years old (n = 102) participated in a randomized pretest-posttest trial. Smokers received a smartphone application (REQ-Mobile) with short messages and interactive tools or a text messaging system (onQ), managed by an expert system. Self-reported usability of REQ-Mobile and quitting behavior (quit attempts, point-prevalence, 30-day point-prevalence, and continued abstinence) were assessed in posttests. Overall, 60% of smokers used mobile services (REQ-Mobile, 61%, mean of 128.5 messages received; onQ, 59%, mean of 107.8 messages), and 75% evaluated REQ-Mobile as user-friendly. A majority of smokers reported being abstinent at posttest (6 weeks, 53% of completers; 12 weeks, 66% of completers 44% of all cases). Also, 37% (25%of all cases) reported 30-day point-prevalence abstinence, and 32% (22% of all cases) reported continuous abstinence at 12 weeks. OnQ produced more abstinence (p<0.05) than REQ-Mobile. Use of both services predicted increased 30-day abstinence at 12 weeks (used, 47%; not used, 20%; p = 0.03). REQ-Mobile was feasible for delivering cessation support but appeared to not move smokers to quit as quickly as text messaging. Text messaging may work better because it is simple, well known, and delivered to a primary inbox. These advantages may disappear as smokers become more experienced with new handsets. Mobile phones may be promising delivery platforms for cessation services using either smartphone applications or text messaging.