SocialSync is a sub-frame synchronization protocol for capturing images simultaneously using a smartphone camera network. By synchronizing image captures to within a frame period, multiple smartphone cameras, which are often in use in social settings, can be used for a variety of applications including light field capture, depth estimation, and free viewpoint television. Currently, smartphone camera networks are limited to capturing static scenes due to motion artifacts caused by frame misalignment. Because frame misalignment in smartphones camera networks is caused by variability in the camera system, we characterize frame capture on mobile devices by analyzing the statistics of camera setup latency and frame delivery within an Android app. Next, we develop the SocialSync protocol to achieve sub-frame synchronization between devices by estimating frame capture timestamps to within millisecond accuracy. Finally, we demonstrate the effectiveness of SocialSync on mobile devices by reducing motion-induced artifacts when recovering the light field.