How do I set up Exchange 2007 Activesync to work with PDAs that can sync to Exchange Server

I have Exchange Server 2007.  We use Outlook Web Access, but some users now want to use ActiveSync to get their email on their PDAs.  I'm looking at Exchange Management Console/Service Configuration/Clicent Access/Exchange Active Sync and see that although I have the Internal URL set up, I do not have an External URL.  I assume that I have to do something other than just pointing the PDA's setup to our "" address?
Does anyone have good instructions on setting up ActiveSync with Exchange Server 2007?
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When you set up your Client Access (OWA) server, ActiveSync is enabled by default. If your CA server is accessible from the world via a domain name (like, you should be able to point your mobile device to that domain and, with proper credentials, it should connect properly.

Depending on the device, you may need to use domain\username as the username, if there is no specific place to enter the domain. You may also need to acquire an SSL certificate that is signed by a root authority, as some devices have a built-in set of root authorities and will refuse to trust anything else. The cert needs to be installed on your CA server.

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