Hi,
I think what you need to do is for each site number, create a call handler, and assign it a 2-digit extension. By default, the minimum extension length is 3 digits, so you'll need to change the following registry key to 2:
HKLM\SOFTWARE\Active Voice\Doh\1.00\Minimum Handler AVP_DTMF_ACCESS_ID length
As always, please be very careful when editing the registry. That key also controls the minimum length of subscriber extensions. Even though Unity SA won't enforce it, you'll still want to keep subscriber extensions at least 3 digits so they don't interfere with private distribution list numbers when subscribers address messages via the TUI.
Now this is all just theory, I haven't tested any of this out. But I think it will work OK.
Nancy