We use Zimbra Open edition. A number of user's have I-Phones or I-Pods. Using i-Cal these devices can alert users to upcoming meetings etc if they are away from their desks. In the UK the latest i-pod is about £180 (you can't get the last generation units any more so there has been a price hike). It seems like a bit much for something my old Palm Pilot did for a fraction of the cost (many years ago - OK it was before Wi-Fi)
I am looking for a Wi-Fi enabled device that would serve as a meeting pager. A Wi-Fi phone with Symbian or Android Pad would seem to be the answer. Some of the Nokia Wi-Fi phones look like they would be OK but no-one seems to be able to confirm i-Cal or CalDAv support. Android seems to be firmly tethered to G-Mail for its Calendaring or too pricy (see the Dell and Samsung devices).