It is no longer just an opinion but a fact that the only way to prevent a catastrophic future for humanity on a planetary scale is to introduce sustainable practices in all areas of human endeavour. The key role in these processes is activity to education. The aim of this study is to investigate the perceptions of Slovenian secondary school students, parents, and teachers (SPTs) regarding the role of smartphones and tablets in promoting 21st-century skills. This study explores the views of Slovenian secondary school students, parents, and teachers (SPTs) on the value of smartphones and tablets in 21st-century skills education. The results show a consensus among participants that smartphones and tablets make a positive contribution to various aspects of 21st-century skills as a Prerequisite for Sustainable Future. Participants consistently rated the suggested benefits of smartphones and tablets above the middle of the scale, with a focus on internet, digital, and information literacy. However, there is still room for improvement in basic skills and higher-order thinking skills. The factorial analysis revealed three correlated factors: Holistic Learning skills, Higher-Level Cognitive skills, and Digital Information Literacy skills. Subsequent analysis revealed significant differences between the focus groups, with students showing stronger agreement with the positive impact of smartphones and tablets on a wide range of skills. While teachers recognized the value of smartphones and tablets for students’ digital literacy and engagement, the differences between teachers and other groups were relatively small. These findings underscore the importance of integrating smartphone strategies and technology tools to promote 21st-century skills as a Prerequisite for Sustainable Future. Educators and policymakers can use these findings to promote effective teaching and learning practices that meet the demands of the 21st century.