Hi Jason,
Here are a couple of ways to change this behaviour;
Changing Message Addressing Settings
Cisco Unity Connection provides two ways for users to address messages to other users when they are using touchtone keys:
Spell a user name.
Enter a user extension.
Regardless of the option you choose here, as users address a message by phone, they can switch between addressing by name and addressing by extension by pressing the # key twice. However, when the Disable Spelled Name Searches check box is checked on the System Settings > Advanced > Conversations page, users can address messages over the phone only by entering user extensions.
Users can also change the message addressing setting that Connection uses by default only in the Cisco Unity Assistant, not by phone.
To Change Your Message Addressing Setting
Note: that you can also change message addressing settings on a user template. Keep in mind that settings on a user template apply only to accounts that are subsequently created from that template.
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Step 1 In Cisco Unity Connection Administration, click Users.
Step 2 On the Search Users page, in the Search Results table, click the alias of the applicable user.
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Note: If the user does not appear in the search results table, set the applicable parameters in the search fields at the top of the page, and click Find.
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Step 3 On the Edit User Basics page, on the Edit Menu, click Playback Message Settings.
Step 4 On the Playback Message Settings page, under Message Addressing, select how the conversation prompts users to address messages to other users:
Spelling the Last Name Then First Name
Entering the Extension
Spelling the First Name Then Last Name
Step 5 Click Save.
Hope this helps!
Rob