Add digit to outbound caler ID

The issue is we have two PBX’s connected with IAX2 trunks that have the same 3 digit numbering scheme. 1XX

In the outbound routes, we add an extra 1 to dial their trunk ex. 11XX. The extra 1 is the stripped going to the trunk.

When someone calles form the remote system, we see the CID 1xx then a name of someone on our pbx

For Example:

(remote pbx) Ext 110 - John Smith
–Calls ext 111 (home pbx)—
111 Rings, Shows CID "110 - Sam Adams (users cid with matching ext on home system)

How can I add an extra digit to the remote pbx outbound trunk?

Is it really that big of a deal to redo one of the pbx extension format? I would simply export all phone extensions on one pbx change them from 1XX to say 2XX then reimport, and using endpoint manager reconfigure all the phones…

I guess you could send the call to a custom context eg in your trunk definition put: context=from-remotepbx (obviously removing context=from-internal )
define that context inside extension_custom.conf

exten => _1XX,1,Set(CALLERID(number)=1${CALLERIDNUM})
exten => _1XX,n,Goto(from-internal,${EXTEN},1)

Havent tested it but it gives you an idea.