Abstract: We included 35 studies, from a wide range of countries on six continents. Nineteen studies were conducted in low- and middle-income settings and sixteen in high-income settings. Some of the studies explored the views of people who had experienced the interventions, whereas others were hypothetical in nature, asking what people felt they would like from a digital health intervention. The studies covered a range of digital targeted client communication, for example medication or appointment reminders, prenatal health information, support for smoking cessation while pregnant, or general sexual health information. Our synthesis showed that clients' experiences of these types of programmes were mixed. Some felt that these programmes provided them with feelings of support and connectedness, as they felt that someone was taking the time to send them messages (moderate confidence in the evidence). They also described sharing the messages with their friends and family (moderate confidence). However, clients also pointed to problems when using these programmes. Some clients had poor access to cell networks and to the internet (high confidence). Others had no phone, had lost or broken their phone, could not afford airtime, or had changed their phone number (moderate confidence). Some clients, particularly women and teenagers, had their access to phones controlled by others (moderate confidence). The cost of messages could also be a problem, and many thought that messages should be free of charge (high confidence). Language issues as well as skills in reading, writing, and using mobile phones could also be a problem (moderate confidence). Clients dealing with stigmatised or personal health conditions such as HIV, family planning, or abortion care were also concerned about privacy and confidentiality (high confidence). Some clients suggested strategies to deal with these issues, such as using neutral language and tailoring the content, timing, and frequency of messages (high confidence). Clients wanted messages at a time and frequency that was convenient for them (moderate confidence). They had preferences for different delivery channels (e.g. short message service (SMS) or interactive voice response) (moderate confidence). They also had preferences about message content, including new knowledge, reminders, solutions, and suggestions about health issues (moderate confidence). Clients' views about who sent the digital health communication could influence their views of the programme (moderate confidence). For an overview of the findings and our confidence in the evidence, please see the 'Summary of qualitative findings' tables. Our matrix shows that many of the trials assessing these types of programmes did not try to address the problems we identified, although this may have been a reporting issue. Our synthesis identified several factors that can influence the successful implementation of targeted client communication programmes using mobile devices. These include barriers to use that have equity implications. Programme planners should take these factors into account when designing and implementing programmes. Future trial authors also need to actively address these factors and to report their efforts in their trial publications.

Plain-language summary: We included 35 studies from around the world. These studies showed that clients' experiences of these types of programmes were mixed. Some felt that these programmes provided them with feelings of support and connectedness, as they felt that someone was taking the time to send them messages (moderate confidence in the evidence). Others also described sharing the messages with their friends and family (moderate confidence). However, clients also pointed to problems when using these programmes. Some clients had poor access to cell networks and to the internet (high confidence). Others had no phone, had lost or broken their phone, could not afford airtime, or had changed their phone number (moderate confidence). Some clients, particularly women and teenagers, had their access to phones controlled by others (moderate confidence). The cost of messages could also be a problem, and many thought that messages should be free of charge (high confidence). Languages issues as well as clients' skills in reading, writing, and using mobile phones could also be a problem (moderate confidence). Clients dealing with stigmatised or personal health conditions such as HIV, family planning, or abortion care were concerned about privacy and confidentiality (high confidence). Some suggested strategies to deal with these issues, such as using neutral language and tailoring the content, timing, and frequency of messages (high confidence). Clients wanted messages at a time and frequency that was convenient for them (moderate confidence). They had preferences for different delivery channels (e.g. short message service (SMS) or interactive voice response) (moderate confidence). They also had preferences about message content, including new knowledge, reminders, solutions, and suggestions about health issues (moderate confidence). Clients' views about who sent the digital health communication could influence their views of the programme, and many people wanted a sender that they knew and trusted (moderate confidence). We searched for studies published before July 2017.