Outlook Mobile Service is a new feature integrated into Microsoft Office Outlook 2007 that allows you to create and send SMS text messages as well as multimedia messages (MMS) to a mobile device from Outlook similar to sending e-mail messages.
By using Outlook Mobile Service, you can send a message both as an e-mail message and as a mobile message to multiple contacts at the same time. The messages are saved in your Sent Items. You can also receive messages from a mobile phone directly in your Outlook Inbox, use a mobile address book that has information about all your mobile contacts, and redirect summaries of your Outlook Calendar to your mobile phone.

Features include:

-Complete integration with Outlook
-Mobile text and multimedia messages sent directly from your computer
-E-mail messages, reminders, and calendar summaries forwarded to your mobile phone
-Both e-mail and mobile messages sent at the same time
-A new mobile address book
-AutoResolve mobile contacts

This service is dependant on your carrier. For now it looks like only some US carriers are supported.