The iPhone became a more acceptable solution for the enterprise with Exchange support added in the 2.0 firmware update and now it looks like support for enterprise solutions is expanding. I just read on The iPhone Blog that Groupwise Synchronization is here via the NotifyLink solution.
My small company has been using GroupWise for several years and this would be a great solution for us, but we are actually moving to Exchange in the next two weeks so I won't be able to try it out myself. However, this is still a very welcome solution for many who no longer have to forward all of their emails to another account to view them faster (just like I had setup). I did have access to a web-based interface, but it is a much better experience to have a solution that works with native applications.
The online User Guide shows you everything you or your IT department needs to set up the server and you will find just a few limitations with the solution, similar to the limitations with Exchange. These includes no task synchronization, no initiation of meeting invites from the iPhone, and no saving attachments to the device. The NotifyLink setup does let you use the native iPhone email, calendar, and contacts applications though so the solution if pretty seamless. Features like remote wipe are also supported.