MS Exchange.org has a good article on Microsoft Exchnage 2003 and the DirectPush technology ….
One of the most interesting features available in Exchange 2003 Service Pack 2 is without doubt the new DirectPush technology (aka AUTD v2), which improves the mobile messaging experience for your end-users by providing close to real over the air (OTA) push technology. In this article, which is the first in a 5 part article series on mobile messaging using Exchange 2003 with SP2 applied and mobile devices running Windows Mobile 5.0 with the Messaging and Security Feature Pack (MSFP) installed, we’ll take a closer look at the new DirectPush technology.
[Via MSExchange.org]