For my own reference..

Exchange 2010 BES Express 5 Configuration
Exchage 2003 is same as for BES Express 4 / BPS, see here.
Exchange 2007 is a bit like 2010, see http://docs.blackberry.com/en/admin/deliverables/14347/Configuring_Exchange_2007_environ_280254_11.jsp

Download / Install Microsoft Exchange Server MAPI Client and CDO 1.2.1 from http://www.microsoft.com/downloads/details.aspx?FamilyID=E17E7F31-079A-43A9-BFF2-0A110307611E&displaylang=en

Add User BESAdmin, with mailbox.
Add BESAdmin to BUILTIN\Administrators group on BES machine

Get-MailboxDatabase | Add-ADPermission -User “BESAdmin” -AccessRights ExtendedRight -ExtendedRights Receive-As, ms-Exch-Store-Admin
Add-RoleGroupMember “View-Only Organization Management” -Member “BESAdmin”
Add-ADPermission -InheritedObjectType User -InheritanceType Descendents -ExtendedRights Send-As -User “BESAdmin” -Identity “CN=Users,DC=YOURDOMAIN,DC=local”

Get-ThrottlingPolicy | where {$_.IsDefault -eq $true} | Set-ThrottlingPolicy -RCAMaxConcurrency $null

New-ManagementRoleAssignment -Name “BES Admin EWS” -Role ApplicationImpersonation -User “BESAdmin”

Notepad \Program Files\Microsoft\Exchange Server\V14\Bin\microsoft.exchange.addressbook.sevice.exe.config, set MaxSessionsPerUser to 100000
Restart Exchange Address book svc

Set-RpcClientAccess –Server YOUREXCHANGESERVER –EncryptionRequired $False

Manually create the GC hostname MAPI registry keys, as per http://www.blackberry.com/btsc/search.do?cmd=displayKC&docType=kc&externalId=KB03304, or use the two reg attached .reg files. This fixes the:
MailboxManager::InitializeProfile – OpenMsgStore (0×80040111)
(followed by)
MailboxManager::SubsystemInitialize – OpenMsgStore (0×80040111)
(followed by)
BlackBerry Messaging Agent Blackberry Agent 1 failed to start. Error code 5305
errors

On Server 2008 x64, SQL Express (2005) will not be installed. Install SQL Express 2008 prior.

Log on as BESAdmin, do the install. BES Express 5 wants you to “name” the Blackberry server, and this should not be the same as the name of the computer itself.

Alternatively, buy an HTC Desire.