Calendar section enables you to plan your doings and make reminding notes. In the current version you are able to read the data from your phone, edit or delete it, add new entries and write changes back to your phone. To read the data from your phone, simply press "Read from phone" button on the toolbar. The tree will be filled with entries contained in phone's memory.
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As you can see, the variety of entries in this section is formed by Meeting, Memo and Anniversary for Nokia and Siemens phones and Appointment, Reminder and All day event for Sony Ericsson phones. As well there is the Deleted items folder to store all the deleted items in and to be able to restore or completely delete them if needed.
Calendar itself consists of two parts Events list and Planner.
See also:
Working with OPMS
Events list
Planner