Why the '!'?
Anyhow, you can't create a message waiting key for a hunt group.
Here's what you do:
Create a different hunt group with the same members - as example we can call it 5555.
Next, delete the 1st member of that hunt group from all phones and reprogram that button as 4444.
Next, in call rerouting forms, forward that button to the new hunt group on a busy to 5555 and RNA back to voice mail.
Now you can put a message waiting key of 4444 on all the phones.
Ralph