Some you would have know about Outlook Mobile Service (OMS) from Outlook 2007, where you get to send and receive text messages directly integrated into Microsoft Outlook 2007 itself. But now in Exhange 2010 beta you can set up OMS directly into the Exchange server by mailbox account. This is done through the Outlook Web Access (OWA) OWA>Options>Settings>Calender>Text Messaging Notification (Figure 1).
Due to that Exchange server 2010 is now still in beta, the list of mobile operaters that coverage is right now limited to only USA & China PRC (Figure 3). But I believe that this list will grow with Exchange 2010 reach RTM.
Also possibly OWA will support 3rd-party OMS provider in the near future or even in RTM (figure 2)