We are looking at how we can support both types of synchronization methods for our prospective clients. Having tested a iPhone with Zimbra Mobile that works straight out of the box. Moving onto a BlackBerry using Funambol to sync with Zimbra we ran into quite a few issues; duplicate calendar entries, appointments being re-sent, appointments being sent with incorrect email address! From researching, the later, I believe the problem occurs when using two calendar sources are configured on the BB.
Which devices do you support for your clients ? What issues have you ran into ? Do you even use ActiveSync clients on BBs ?