Formulating short form advertising messages with little ad content that work and choosing high-performing channels to disseminate them are persistent challenges in multichannel marketing. Drawing on the persuasive systems design model, we conducted an experiment with 33,848 actual customers of an international telecom company. In a real-life setting, we compared the effectiveness of three persuasion strategies (rational, emotional, and social) tested in three marketing channels (short message service, social media advertising, and mobile application), evaluating their effect on influencing customers to purchase international mobile phone credits. Results suggest that companies should send rational messages when using short form advertising messages regardless of the channel to achieve higher response rates. Findings further show that certain customer characteristics are predictive of positive responses and differ by channel but not by message type. Findings from crowdsourced evaluations also indicate that people noticeably disagree on what persuasive strategy was applied to these short messages, which might indicate that consumers are not well-equipped to identify persuasive strategies or that what advertisers see as a ‘pure’ strategy actually involves elements from multiple strategies as interpreted by consumers. The results have implications for the theoretical understanding of persuasive short form commercial messaging in multichannel marketing and practical insights for advertising within limited amount of space and attention afforded by many digital channels.