Changing default voicemail prompts

Currently we run voicemail(su)

Instead of it default to “the person at extension xxx is unavailable” I want it to just say “the person is unavailable”. Is there any way to change the global default unavailable message. And yes I am aware that users can set their individual voicemail preferences, I specifically want to change the default so that it does not say “at extension” or the extension itself.

Thanks for any help!