Abstract Problem Utilization of available maternal health services is comparatively low among adolescent population in Dhaka urban slum areas and lack of adequate knowledge is one major contributor to low service utilization among slum dwelling adolescent mothers. Description of problem Dhaka urban slum dwelling female adolescents are difficult to reach adequately with health messages through traditional home visit by community health workers for counseling, because many of these adolescents in Dhaka urban slums have a job outside home. We designed and implemented an innovative health communication intervention “Health Boost” - an approach to provide reproductive, maternal and newborn health information for married female adolescents using the voice message system on mobile phone. Methods We delivered ‘Health Boost’ (HB) voice messages to enrolled married adolescent girls, twice a week, with re-listening option. Pregnant and non-pregnant participants received separate sets of messages. Enrollment was started after baseline survey (September 2016) and continued during October 2016 - April 2017. Pregnant participants received messages at least for 6 months before delivery. For evaluation, we followed pre-post observation study design and had the endline survey in November 2017. Results Comparing HB non-receivers at baseline (n = 321) and HB receivers at endline (n = 45), statistically significant improvement was revealed for knowledge on danger signs - (a) during pregnancy (55.5% vs. 93.3%; p < 0.001), (b) during child delivery (54.2% vs. 82.2%; p < 0.001), (c) for newborn (56.7% vs. 75.6%; p < 0.02). We also found significantly higher utilization of service among HB receivers: Utilization of antenatal care increased from 70.4% to 87.5% (p < 0.02); and use of postnatal care increased from 31.6% to 73.7% (p < 0.03). Lessons ‘Health Boost’ messages were instrumental and effective to increase knowledge and service utilization among married adolescent girls in Dhaka urban slum areas. Key messages Voice message is an innovative way to reach hard-to-reach population by using mobile phone technology. Voice messages were instrumental and effective to increase knowledge and service utilization among urban female adolescent population, for reproductive, maternal and newborn health.