Embodiments are directed to activation and performance of multiple-subscriber-identity-module (“multi-SIM”) automatic synchronization of mobile devices. A user may specify one or more data types for which multi-SIM automatic synchronization should be performed, which may include incoming calls, sent text messages, and the like. Information about an answered incoming call may be sent from a first mobile device to at least one additional mobile device so that the at least one mobile device may update at least one call log and may remove at least one notification for the call accordingly. When multi-SIM automatic synchronization is performed for sent text messages, the first mobile device may send a copy of the sent text message to the at least one additional mobile device so that the received copy may be stored in the sent messages folder of the at least one additional mobile device.