Similar to the previous post regarding provisioning iPhones for Exchange servers, the same can be done with Windows Mobile (though I don’t yet know how this will changes with Windows 7 Mobile). I haven’t found a nice utility to do this, so your relegated to hand coding a .xml file, but it’s no biggie.
If your situation is similar to mine, you have many remote users with mobile phones. There are times when they need to replace the phone while traveling or something else happens that requires resetting up the phone to connect to your mail server. We require our self-signed certificate to be installed on the phone, coupled with needing to know all the settings it can be frustrating to help setup a phone, over a phone.