Message-based synchronization is performed at the package level. The generated package database class provides methods for starting and stopping the background processing of the incoming messages.
To start background synchronization:
[SampleApp_SampleAppDB startBackgroundSynchronization];
To stop background synchronization:
[SampleApp_SampleAppDB stopBackgroundSynchronization];
When an incoming message is processed, callbacks are triggered. See Reference: Administration APIs > iPhone Client Object APIs > Message-Based Synchronization APIs > Callback Handlers for information on how to register a callback handler.