Core Issue
The caller ID that needs to be displayed is not the extension, but the main office number. Entering the desired phone number in the external phone number mask and rebooting the phone does not affect the displayed caller ID.
Resolution
In order to resolve this issue, you can use these locations in the CallManager Administration to configure caller ID:
- Directory Number Configuration page Scroll down to External Phone Number Mask and enter the number that you want to send to the PSTN. Then click Update at the top of the page. You have to repeat this same procedure for the other extensions configured for this IP phone (if you want to send those numbers to the PSTN).
- Route Pattern Configuration page Locate the route pattern that you are using to make calls to the PSTN. Scroll down to the Calling Party Transformations section.
- If you check Use Calling Party's External Phone Number Mask, you use the number that you configured in the Directory Number Configuration page as the caller ID.
- If you uncheck Use Calling Party's External Phone Number Mask, then you can configure the Calling Party Transform Mask. Enter a number such as 978858xxxx (CallManager fills out the xxxx with the phone's 4-digit extension).
- Route List Detail Configuration page Go to the Calling Party Transformations section.
- Use Calling Party's External Phone Number Mask If you set this to On, you use the number that you configured in the Directory Number Configuration page as the caller ID. If you set it to Off, then you need to configure the Calling Party Transform Mask (next line on this same page). The setting that you use here overrides the settings that you configured in the Route Pattern Configuration page. You configure the Calling Party Transform Mask here in the same way as explained for the Route Pattern Configuration page.
For more information, refer to these documents: