I'm posting this in case someone else needs it sometime as it took me a while to find.
I have a personal home Exchange server account and a work Exchange server account. I wanted to be able to synch my home and work contacts and calendars (don't use work Tasks and just want personal email). I had a really difficult time trying to find a way to do this, and after looking at multiple third-party products still couldn't find a way.
But then I found some information about WM6 that indicated Microsoft had added a new cross pollination registry setting that was defaulted to prohibiting 2 Exchange server accounts from being sync'ed. I changed the registry setting and now it works just as I wish. My home Exchange account syncs wirelessly/push and I can BT or cradle dock my Treo 750 at work and all 3 get synced up together. Nice. Didn't even cost me a penny.
Here's the short of it:
Synchronizing a specific information type with two PCs at the same time is referred to by Microsoft as "non local cross pollination". With Windows Mobile 6, Microsoft introduced a new registry setting that enables or disables this feature. The key is a REG_DWORD key at the following location:
HKEY_CURRENT_USER\Software\Microsoft\ActiveSync\EnableNonLocalCrossPollination
The default value is "0" which disables the feature. Changing the value to "1" will allow you to select multiple computers to be synchronized.
Do a soft reset and configure ActiveSync on your device to use both computers for syncing and you're good to go.
The full article/instructions can be found at:
http://www.bitshift.ch/eng/support/kbase/000003.asp
Hope this helps someone else one day...great way to sync a calendar on multiple computers, etc.