This is actually QUITE simple. I would say to do this in a maintenance time period. Shut down the BES services on your current server. Install BES 3.6 onto the new server using the same SRP and the same Virtual Server name (for instance PRODBES11) and the same service account mailbox. Install service packs for the BES. Once you start up the server, it will populate the users and settings from the service account mailbox.
Thats really all there is to it. You can actually leave the current production server up and running during the installation processes, as the installation and service pack patching *shouldn't* start up the services (although I have NEVER trusted this). You will want to keep it on the current SRP for less intrusiveness to your users. If you use a second SRP, they will have to recradle/reauthenticate their handhelds (which is a pain in the ass). Downtime for the users is likely no more than 1 hour max, if you know what you're doing.
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