With Outlook 2010 or iPhone OS 4.0 it is possible to access multiple mailboxes / Exchange accounts. There is no need to create multiple Outlook profiles. So the access to mailboxes from different Exchange organizations is possible too.
You might use a personal mailbox and a department's mailbox. So now you can send as yourself or as department - and you will send with the different senders address!
Note: Please keep in mind that the reply to a mail which was moved from mailbox 1 to mailbox 2 are sent back to the original mailbox.
By default you can configure three mailboxes with this feature. If you create this registry key you might configure access up to 15 mailboxes
HKCU\Software\Policies\Microsoft\Exchange, create 32 Bit DWORD "MaxNumExchange" and insert decimal value 1 to 15. With Office 2010 GPOs this configuration might be distributed all over the company.
Mails which are sent by the other account are stored in sent items folder of this account. That's nice, eh?