Mobile phones are increasingly used to facilitate in-service training for frontline health workers (FLHWs). Mobile learning (mLearning) programmes have the potential to provide FLHWs with high quality, inexpensive, standardised learning at scale, and at the time and location of their choosing. However, further research is needed into FLHW engagement with mLearning content at scale, a factor which could influence knowledge and service delivery. Mobile Academy is an interactive voice response training course for FLHWs in India, which aims to improve interpersonal communication skills and refresh knowledge of preventative reproductive, maternal, neonatal and child health. FLHWs dial in to an audio course consisting of 11 chapters, each with a 4-question true/false quiz, resulting in a cumulative pass/fail score. In this paper, we analyse call data records from the national version of Mobile Academy to explore coverage, user engagement and completion. Over 158 596 Accredited Social Health Activists (ASHAs) initiated the national version, while 111 994 initiated the course on state-based platforms. Together, this represents 41% of the estimated total number of ASHAs registered in the government database across 13 states. Of those who initiated the national version, 81% completed it; and of those, over 99% passed. The initiation and completion rates varied by state, with Rajasthan having the highest initiation rate. Many ASHAs made multiple calls in the afternoons and evenings but called in for longer durations earlier in the day. Findings from this analysis provide important insights into the differential reach and uptake of the programme across states.