With Exchange Server 2010 calendar permissions can be managed using the *-MailboxFolderPermission cmdlets. While these cmdlets can be used to manage permissions on any mailbox folder, we`ll focus on calendar permissions.

In fact we got 4 *-MailboxFolderPermission cmdlets in Exchange Server 2010:

 

Example:
This will give user Johan Reviewers rights on Mattias calendar.

Add-MailboxFolderPermission -identity “Mattias:\calendar” –user “Johan@example.com” -AccessRights Reviewer

Types of diffrent permission to set:
In this example above I use reviewer.  However, instead of using “Reviewer” permissions you may choose from all these different types of permissions:
None                                                   FolderVisible
Owner                                                CreateItems, ReadItems, CreateSubfolders, FolderOwner, FolderContact, FolderVisible, EditOwnedItems, EditAllItems, DeleteOwnedItems, DeleteAllItems
PublishingEditor                         CreateItems, ReadItems, CreateSubfolders, FolderVisible, EditOwnedItems, EditAllItems, DeleteOwnedItems, DeleteAllItems
Editor                                                CreateItems, ReadItems, FolderVisible, EditOwnedItems, EditAllItems, DeleteOwnedItems, DeleteAllItems
PublishingAuthor                       CreateItems, ReadItems, CreateSubfolders, FolderVisible, EditOwnedItems, DeleteOwnedItems
Author                                              CreateItems, ReadItems, FolderVisible, EditOwnedItems, DeleteOwnedItems
NonEditingAuthor                      CreateItems, ReadItems, FolderVisible
Reviewer                                          ReadItems, FolderVisible
Contributor                                    CreateItems, FolderVisible

The following roles apply specifically to calendar folders:

AvailabilityOnly                        View only availability data
LimitedDetails                            View availability data with subject and location

 

Links:

http://www.n2networksolutions.com/2011/02/22/manage-exchange-2010-calendar-permissions-using-powershell/

http://blog.powershell.no/2010/09/20/managing-calendar-permissions-in-exchange-server-2010/