...with Macs can't do it from within a browser, because OWA is feature-limited except in Internet Explorer (same problem exists for Windows users who prefer other browsers)... Exchange Activesync will only "push" an individual user's main calendar to mobile devices, and the only way to synchronize a common "Public Folder" calendar with an individual user's calendar is for the individual user to do it repetitively and manually.
One of the hospitals we use has the same stupid Exchange calendar Activesync issues as described. Instead of syncing from Exchange, it is actually faster to manually enter my on-call dates into Google Calendar (which my practice uses across multiple users, devices and platforms). I wonder how many times Microsoft is going to have to be pummeled by Google before they wake up...or die.
