Microsoft Global Contact Access for Windows Mobile powered devices.

With Microsoft Global Contact Access, you can use Pocket Outlook on your Windows Mobile powered Smartphone or Pocket PC Phone Edition to look up contacts in the Global Address List (GAL) on your corporate Exchange server.
You can also check your co-workers' schedules to see if they're free or busy, and add multiple recipients to a meeting request.

Even if you're away from your office you'll have all the information you need to connect with any co-worker in your organization, and send them e-mail or request a meeting.