MSDN - Configuring Exchange Impersonation in Exchange 2010
MSDN - Configuring Exchange Impersonation (Exchange Web Services) for Exchange 2007. See also: Sumatra's Calendar Server Blog - Exchange 2007 Impersonation - Debugging Protocol

Microsoft Office 365 Community - Forums - Manage Office 365 - Distribution Group permissions to a Mailbox or Calendar using PowerShell? “You can grant permissions to a distribution group just as you would a user, but you'll first need to turn that distribution group into a security group. That allows it to carry permissions and then share those permissions to the members of the group.”

superuser - How to setup Calendar permissions for group to group