Background: While a significant breast cancer burden exists for Korean American immigrant women, their cancer screening behavior is strikingly poor, and few interventions have focused on this population. To promote breast cancer screening behavior in Korean American immigrant women, a mobile phone multimedia messaging intervention (mMammogram) was developed. Objective: The current study explores the impact of mMammogram on changes to study participants’ screening behavior and proposes suggestions for how the intervention can be improved for wide dissemination and implementation in the Korean American community. Material and Methods: Data were collected through qualitative research methods. Three focus groups were conducted with 14 Korean immigrant women who completed the mMammogram. Findings: Three themes emerged: (1) better understanding of breast cancer and screening through mMammogram (e.g., increased knowledge on breast cancer and screening methods, increased understanding of the importance of regular mammography, and reduced anxiety about mammography); (2) health navigators as a trigger to promote mammography (e.g., providing resources for free or low-cost mammograms and scheduling mammogram appointments); and (3) suggestions for mMammogram (e.g., technical issues and program period). Conclusions: Mobile app intervention that is culturally tailored, along with health navigation services, can be a feasible, effective, and acceptable tool to promote breast cancer screening behaviors in underserved immigrant women. A mobile app can cover a broad range of breast cancer health topics and the health navigator can further help women overcome barriers to screening. A health navigation service is critical in overcoming language, transportation, and health accessibility barriers and triggering a positive change in their health screening behavior, especially for newly arrived immigrant populations.