A method and system is disclosed for starting a server-initiated synchronization session between a mobile device and a server system. The server system and the mobile device communicate through a first communication channel for the synchronization session. After detecting that a predetermined set of data items are ready to be synchronized with the mobile device, the server system sends a notification message informing the mobile device to start a synchronization session through a second communication channel. Once receiving an initiation message from the mobile device to start the synchronization session, the server system starts to send the data items to the mobile device through the first communication channel.