Deploying a Microsoft Server 2008 R2 with Microsoft Exchange 2010 into an existing MS Server 2003 / Exchange 2003 environment has some challenges, but when you add in a Blackberry it takes a little foresight.
When a client has an old version of BES or is using Blackberry Professional Server, they should know in advance that it will NOT work with Exchange 2010 – unless they keep the BES account on the legacy (2003) server and the mailboxes of each of the users who will be using a BB.
BIS is also sketchy with Exchange 2010 and OWA. Be well aware that you can’t decide to just dump the BES or Blackberry Professional Server and use BIS & the OWA on your Exchange 2010 server, as it probably won’t work.
What WILL work?
As mentioned, keeping the mailboxes of BB users and the BES mailbox itself on the legacy server…
Upgrading to the latest version of Blackberry Enterprise Server.
Optionally you could just sit back and wait until the recently announced Blackberry Enterprise Server Express is released before moving to Exchange 2010
Other things to consider might be your Anti-Virus / Exchange Anti-Virus/Spam solutions. In our case, Trend Micro Worry Free Security Advanced 5.0 had to be upgraded to WF 6.0, then patched with the service pack. And the messaging protection would not work either, so Trend gives you a free version of their ScanMail to use until WF 7.0 is released. That will be a phone call to Trend to obtain.
Backup Exec 12.5 and below does not fully support Server 2008 R2 and Exchange 2010. So you will need another solution for this.
Other than those few issues, we are very pleased with the Microsoft Server 2008 R2 and Exchange 2010 combination. This is our first experience with a production environment and we are looking forward to the next one!