Aims To test the population impact of offering automated smoking cessation interventions via the internet and/or by mobile phone. Design Pragmatic randomized controlled trial with five conditions: offer of (i) minimal intervention control; (ii) QuitCoach personalized tailored internet-delivered advice program; (iii) on Q, an interactive automated text-messaging program; (iv) an integration of both QuitCoach and on Q; and (v) a choice of either alone or the combined program. Setting Australia, via a mix of internet and telephone contacts. Participants A total of 3530 smokers or recent quitters recruited from those interested in quitting, and seeking self-help resources ( n = 1335) or cold-contacted from internet panels ( n = 2195). Measurements The primary outcome was self-report of 6 months sustained abstinence at 7 months post-recruitment. Findings Only 42.5% of those offered one of the interventions took it up to a minimal level. The intervention groups combined had a non-significantly higher 6-month sustained abstinence rate than the control [odds ratio ( OR) = 1.48; 95% confidence interval (CI): 0.98-2.24] (missing cases treated as smokers), with no differences between the interventions. Among those who used an intervention, there was a significant overall increase in abstinence ( OR = 1.95; CI: 1.04-3.67), but not clearly so when analysing only cases with reported outcomes. Success rates were greater among those recruited after seeking information compared to those cold-contacted. Conclusions Smokers interested in quitting who were assigned randomly to an offer of either the QuitCoach internet-based support program and/or the interactive automated text-messaging program had non-significantly greater odds of quitting for at least 6 months than those randomized to an offer of a simple information website.