This one has me stumped and I can't find any supporting documentation, so I'm hoping someone out there has some tricks in their bag to share. One of my customers aquired a competitor and both organizations were already running BES 4.1. These are separate forests (two-way trust), with one organization running BES 4.1.7 in an Exchange 2007 environment and the other organization running two BES 4.1.X servers (4.1.6 and 4.1.4) in an Exchange 2003 environment.

The decision was made to migrate everything to a new AD forest, running everything at its current versions (Server 2008 R2, Exchange 2010, etc). Nothing has been migrated yet, but the plan is to migrate users/mailboxes with Quest migration tools, but is there a supported method to migrate the BES users? As their AD account and mailbox will be migrated, I really just need to find a way to re-associate their handhelds with the new BES server(s) (may or may not do a BES 5.0 cluster).

Last I counted, the BES user breakdown was as follows:
4.1.4 - 31 users
4.1.6 - 71 users
4.1.7 - 35 users

I'd really prefer not to re-activate every single one if at all possible. If these need to be upgraded to 5.X in order to move them, I have no issues with that, I just need to put together an action plan.

Thoughts?

BES 5.0 supports an Exchange Resource Forest configuration.

Good article on Exchange resource forest config
Deploy Exchange 2010 in an Exchange Resource Forest Topology: Exchange 2010 SP1 Help

Multiple AD forests should be ok as long as

1) There is a two way trust between them
2) They are all within the same Exchange organization

These are 3 separate forests, which I interpret as 3 separate Exchange organizations (Exchange organization cannot span multiple forests, right?). The first two were completely separate companies until one acquired the other. The third is the new forest they are migrating the original two to.

if not in the same exchange org, its a wipe device to remove encryption keys so you can put it on the new BES. Lucky you only have under 200 users. i know some that had to do this for 1000s

You can turn off wireless backup on BES (if your policy allows it) so users can backup all their stuff, wipe, do selective restore and activate on new BES.

Ugh. Deep down, I knew that was the answer...I just didn't want to believe it. Thanks for confirming what I was afraid of :-p