I’m guessing that you are new to this system and the previous admin caused the trouble you are seeing.
Way back when, someone thought it was a good idea to require dialing 9 before an external number, probably because the legacy system it replaced required the 9, so it minimized user retraining. Well, one problem this causes is that an incoming call from 903736XXXX (answered on an extension) would display the caller ID as 903736XXXX; returning the call from device history would fail because it lacked the initial 9. So, he fixed that e.g. with a custom context that prefixes a 9 before the incoming caller ID.
If my hunch is correct, when 903736XXXX calls, it shows on the extension as 9903736XXXX. But you then have the problem that when used as a caller ID for follow-me, you have to remove the initial 9 that was just added. You can do this with a ‘hook’; see
However, the clean fix is to get rid of all this nonsense and dial numbers the same as you would on a landline or mobile phone. In addition to avoiding various technical issues, it greatly reduces human errors. If you have legacy devices that can’t easily be reprogrammed such as an alarm panel or fax machine speed dial, you can set up the Outbound Routes so that an initial 9 is accepted, though not required.
In any case, make sure that both 911 and 9911 work properly.
If my analysis was completely wrong, please explain how the 11 digit caller ID comes about.