We do not use the Groupwise calendar, so unfortunately I cannot assist you with solving that problem. We use the Oracle Calendar, and to sync that to my iPhone, I export an icalendar file (.ics) from there, and then import it in to iCal at home on my Mac. A little tedious, but it works. I would suggest that you export a file from Groupwise calendar and import it in to Outlook if you are a Windows user.
As far as getting Groupwise to work, it was just a matter of configuring my iPhone properly with the correct servers. Although I've had some problems sending out mail when I am on EDGE. Retrieving mail is not an issue, but there are some issues with outgoing mail.