Microsoft has released a new client-side hotfix (KB 939184) for Outlook 2007 which will allow Outlook 2007 to contact the Exchange 2007 Autodiscover using DNS SRV records (KB 940881). This allows you to save costs by using a single-name certificate with a single IP. A con to this is your Outlook 2007 clients will have to accept a re-direct message. This hotfix will be included in Outlook 2007 SP1.
https://support.microsoft.com/kb/940881 (How to configure)
https://support.microsoft.com/kb/939184/ (Information about hotfix)
https://support.microsoft.com/gp/CUHotFix_LandingPage_Request (Request hotfix)
https://msexchangeteam.com/archive/2007/09/21/447067.aspx (Msexchangeteam.com article)