Objectives: The aim of the study was to compare the response rates and costs of phone call vs. short message service (SMS) screening reminders to prospective randomized controlled trial (RCT) participants. Study Design and Setting: This study was a randomized evaluation within a large Australian diabetes prevention RCT. Participants were men aged 50–74 years, overweight or obese, without a previous type 2 diabetes diagnosis. Those eligible on a prescreening questionnaire who did not attend a further screening assessment within 4 weeks were randomized to receive an SMS or phone call reminder (N = 709). The primary outcome was attendance for further screening assessment within 8 weeks of prescreening. Results: Attendance was 18% (62/354) in the SMS reminder group, and 23% (80/355) in the phone reminder group, with no statistically significant difference in response according to reminder type (relative risk = 1.29, 95% confidence interval [CI]: 0.96–1.73, P = 0.09). The lower confidence limits for response to SMS (95% CI: 14–22%) and phone reminders (95% CI: 18–27%) did not include the 8-week attendance rate before this evaluation, 12%. Phone reminders cost substantially more than SMS reminders (AU$6.21 vs. AU$0.53 per reminder). Conclusion: SMS reminders were as adequate a method as phone reminders to boost RCT screening uptake and were considerably more affordable.