For those who are upgrading to SharePoint 2010 might want to make use of the 2-way synchronous “Connect to Outlook” feature. However, most likely you or your team may have already existing calendars on Outlook to manage different events for different teams. While SharePoint doesn’t have an easy way to connect your existing Outlook calendar, there is a way to get the same end result accomplished with a few steps.
Step 1: Connect your SharePoint calendar to outlook by going to your calendar, and clicking on the Connect to Outlook button under the Calendar Tools > Calendar tab.
Hit Allow in the prompt that appears and then Yes to connect the calendar to Outlook.
Step 2: With both calendars open side-by-side, click on the View tab at the top and change the view to List view.
Do this for both calendars.
Step 3: You should have both calendars on List view now.
From here, you will be able to copy all of the events from one calendar over to the other.
Once this is complete, your old calendar will have now been copied over to the SharePoint calendar and is automatically 2-way synched with the server. Meaning from hereon forth, you and your team can start working on the SharePoint calendar in Outlook or on SharePoint and it will automatically sync up.