Adding a calendar from a 365 user/resource to an on-prem user can be troublesome. Equally, adding a shared calendar to your iphone can be handy. This is easy to do once you've done it once.
Preparing for Office 365
Office 365 Takes over where BPOS finishes off. There's a lot to take in, and a lot of changes. I took a lot of notes, I've noted them here.
Luke Darby 