The WP8 client should be out pretty soon, saw that early access started recently.
But if you are looking at other MDM vendors in hope of efficiently & diversely managing Windows Phone 8 devices, you will be sorely disappointed. Even Airwatch (who teamed up with Nokia recently) can't provide the iOS / Android extended MDM functions, they just aren't available on any software for this platform at the moment. At least no vendor that I'm aware of really has working solutions to be implemented right now.
Some rumors about future updates and improved documentation from Microsoft / Nokia are out there, but I'd say don't get your hopes too high before the next major platform facelift. Before that, you are pretty much stuck with passcode settings, advertising preferred apps in the company hub and Exchange account settings. The polling period design pretty much kills MDM solutions if you have to send multiple commands to the device in a real hurry (one command / polling cycle, cycle of 1 hour normally). Guess Microsoft wanted to give their Intune an advantage or something.