[asterisk-users] Determining extension's sip.conf default mailbox

[Steve Johnson]

Hello list,

How can you obtain the default mailbox for a SIP extension (as stored
in sip.conf and shown with "sip show peer <ext>")?  Is there a
function to extract it?

Why?  Some extensions have shared mailboxes and others do not and I
don't want to duplicate logic, just use the extension's default
mailbox as coded in sip.conf.

sip.conf
----------
[100]
mailbox=100

[102]
mailbox=102

[103]
mailbox=100

I want a function which I can use in the dialplan (1.6) that works like:
DefaultMailbox(100) -> 100
DefaultMailbox(102) -> 102
DefaultMailbox(103) -> 100

for example:
exten s,n,VoicemailMain(DefaultMailbox(${CALLERID(num)}))

Suggestions?
Thanks!