[mirmujahed]

The document which you mentioned i.e. KB22601 , does not mention whether we should first move the service account mailbox to 2010 or the BB user mailboxes.
Also, it is not very clear whether both 2003 and 2010 users will work simultaneously.
Please correct me if I am wrong.
Also, could you please confirm if task 4 ( throttling policy ) and task 6 ( Increase the maximum number of connections to the Address Book service ) are compulsory to apply.

Thanks.