The last few SBS 2008 to Exchange 2010 migrations we've done have caused ActiveSync to break. In terms of breaking, I mean that all ActiveSync devices stop syncing. The partnership is still there on the device, but when we look in Exchange, it knows nothing about the device - no partnerships are listed.
All we need to do is remove the partnership from the phone and re-set it up and then all is fine. This happens on Droid and iOS.
We have another migration coming up next month and would prefer not to have this happen. We've NEVER had this issue on an Exchange 2003/2007 to Exchange 2010.
Any suggestions? Unfortunately, we really don't have anything to troubleshoot, yet. . .