If goal is to just use hosted Exchange instead of the SBS Exchange then it can be done by uninstalling Exchange on the SBS and then changing your MX records to point to the hosted Exchange servers. I'm not aware of any sync from AD to an outside Exchange provider, mainly because it would have to be supported by the hosted Exchange provider also.
Exchange installs by default on SBS 08, it cannot be de-selected in the SBS install but can be uninstalled afterward.
The MS method below doesn't quite work, but the following steps get around the problems.
Remove the all mailboxes by Disabling them: In the Exchange Mgmt Console, select the/any mailboxes, right click and select disable. (Note: Deleting Mailboxes will delete the user, not helpful unless the server is brand new w/out any users.)
Remove the Public Folder replicas:
These steps aren't perfect but you can find them and manually delete instead of moving.
If that fails then use this PS script to remove them:
Open Exchange 2007 management shell (CMD line) and type following commands:
Get-PublicFolder -server xxxxx "\" -Recurse -ResultSize:Unlimited | Remove-PublicFolder -server xxxxx
Get-PublicFolder -Server xxxxx "\Non_Ipm_Subtree" -Recurse -ResultSize:Unlimited | Remove-PublicFolder
-Server xxxxx -Recurse -ErrorAction:SilentlyContinue
Replace xxxxx with your Exchange server name in the above command.
Delete the Public Folder Store using above link.
Delete the Send & Receive Connectors in the Exchange Console.
4.5 If the next step fails with an error "Public folder database contains an address book" then in the Exchange Console expand the organization configuration, and Remove the default Address Book from the offline address book tab.
Setup the reg key so the Mgmt Console can be uninstalled:
Uninstall Exchange from Control Panel, Programs, reboot.
Delete the reg key so SBS/AD doesn't think Exchange is still installed, use link above for instructions.
Remove OWA website from IIS.
Remove the Exchange Administrators Group from AD.
Configure the MX records for the Exchange host.
Consider adding an Autodiscover.domain.com in your DNS, it can simplify Outlook configuration.