With the introduction of Call Answering Rules in Exchange UM 2010, you can dictate how incoming phone calls should be handled, thus enriching the call answering experience of your callers. Out-of-the-box, there are no Call Answering Rules created for you. All your callers will get the same default, call answering experience provided by UM 2007, i.e., callers will be prompted to leave you a voice message. Users who are satisfied with the default experience can continue to retain the same experience without the need to create any rule. This post walk through the steps of creating a simple "default" call answering rule - one that is applied to all inbound phone calls.

Full Article: Exchange Blog