please post more info on..
a) Number of devices
b) Models of devices - so we can guess whether 4.0 or earlier s/w in the handheld
c) Version of Exchange and O/S
d) Maximum permissable outage period to get the change happening in.
e) are they generally a SQL shop...do they have SQL licensed and skills..
several main options including..
1) run up copy of current BES on new HW and move users across - refer here for how to do it.
Livelink - Redirection then once in place do an in-situ upgrade.
2) Requires a secondary temp SRP ID, but then install the new version on the new HW with the temp SRP ID. Move the users across (manually) to the new machine. Once completed remove SRP info from old bes, turn off. Stop all sevices on new BES, replace temp SRP with new SRP and re-start services.
1) Is potentially riskier as your doing the in-situ upgrade and I've had one go wrong on me that was a beatch to recover from (start from scratch), but generally most go fine.
2) 2 is a pain in the ass in terms of the second SRP and then manually moving users. However does mean that you can pace the rollout, perhaps upgrading devices at the same time. This option also is easier to implement the "move to SQL" as part of the process. i.e. you install from scratch and go sql not msde