create new call handler and set it as open greeting..
Step 1 
In Cisco Unity Connection Administration, expand Call Management, then select System Call Handlers.
Step 2 On the Search Call Handlers page, select Add New.
Step 3 On the New Call Handler page, enter basic settings, as applicable. (For field information, on the Help menu, select This Page.)
Note Fields marked with * (an asterisk) are required.
Step 4 Select Save.
Step 5 On the Edit Call Handler page, continue entering settings for the call handler.
Step 6 When you have finished entering settings on the Edit Call Handler page, select Save.
Step 7 On the Edit menu, select any (or all) of the following related pages, to continue adding applicable settings to the new call handler:
•Transfer Rules
•Caller Input
•Greetings
•Message Settings
•Call Handler Owners
Note Depending on how you set up the call handler template on which this new call handler is based, you may not need to change any settings on these additional pages. At a minimum, however, you should record a name and one or more greetings for the call handler.
Step 8 If you change any of the settings on a page listed in Step 7, select Save before leaving the page.
