When you edit a mailbox via the Administrators mailbox it will ask you at the end for a Technicians Function Code (twice)
These control the canned prompts for ... is busy or ... is away
It can be found in the Manual Under:
Program Embedded Voicemail
Programming by Telephone
I will cut and past from the manual but I don't know if it will translate well. I will not be retyping this so if it is unreadable then RTFM.
[tt]Busy Options
The following table describes the behaviour when the mailbox is set up—that is, a name and personal greeting have been recorded by the mailbox owner.
If the mailbox is NOT setup, the fixed system message, "I'm sorry..." followed by the mailbox number and "...is currently on the phone" plays instead of the mailbox name and personal greeting.
Greeting Option Plays...
0
(default) the following fixed system message in both the primary and alternate languages if Bilingual operation is enabled and the caller has not chosen a language:
"I’m sorry, the person you are calling is currently on the phone" followed by the mailbox owner's personal greeting, then the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options.
If Bilingual operation is disabled, the following plays:
"I’m sorry…" followed by the mailbox owner's name, then "...is on the phone" and the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options."
1 "I'm sorry…" followed by the mailbox owner's name, then "...is on the phone" and the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options."
2 the fixed system prompt ("I'm sorry...") as per Option 1, followed by silence instead of "Begin speaking after the tone...".
3 the fixed system message, "I'm sorry, the person you are calling is currently on the phone." followed by the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options."
4 the fixed system message, "I'm sorry, the person you are calling is currently on the phone." followed by silence.
5 the currently selected Non-Busy Greeting option. For example, if the Non-Busy Option is 0, then callers encountering a busy extension will hear the same greeting heard when the extension is not answering or call forwarded always to voice mail
6 a standard greeting as per Option 5 minus the mailbox user's name, followed by the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options."
7 a standard greeting as per Option 6, followed by the leave-message tone, and then silence.
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What's most important is that you realise ... There is no spoon.