Smartphones equipped with high-resolution lenses and advanced photo processing capabilities have evolved into versatile, multifunctional devices. This paper introduces a novel method for extracting and analyzing rock mass discontinuities using smartphones, encompassing smartphone photography, ground control point selection, point cloud reconstruction, and discontinuity set identification and analysis. The method was validated through a slope case study in Bayi District, Linzhi city, Tibet, China, under natural light and a tunnel case study in Northwest China under artificial light, and the results agreed well with traditional compass measurements. Notably, the method proved efficient, reducing the measurement time to 15 min compared to 1.5 h with a geological compass in Case 1. Significant insights were gained regarding the impact of photo quantity and shooting distance on point cloud accuracy, along with the influence of lighting in tunnel environments, thus offering valuable guidance for fieldwork. Moreover, the potential of this smartphone-based method was confirmed through comparative analysis with laser scanner data. In summary, rock mass measurements using smartphones are validated as simple, efficient, and practical approaches for geological studies.