Cisco CUCM and Caller ID / CLID sending

I don't know where I scraped up this information originally, but it now seems to live at: https://supportforums.cisco.com/docs/DOC-1861

How to send / places to configure CLID (caller id) from Cisco CUCM
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1.  "Directory Number Configuration" page.

Scroll down to "External Phone Number Mask". Enter here the number that you want to send to the PSTN. Then click on "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 also to the PSTN).
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2.  "Route Pattern Configuration" page.

Locate the route pattern that you are using for doing calls to the PSTN.

Scroll down to the "Calling Party Transformations" section.

- If you check the "Use Calling Party's External Phone Number Mask" checkbox, you will use the number that you configured in the "Directory Number Configuration" page as caller ID.

- If you uncheck that checkbox, then you can configure the "Calling Party Transform Mask". Just enter here a number like, as an example, 978858xxxx (CUCM will fill out the xxxx with phone's 4-digit extension).
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3.  "Route List Detail Configuration" page.

Go to the "Calling Party Transformations" section.

If you set "Use Calling Party's External Phone Number Mask"  to "on", you will use the number that you configured in the "Directory Number Configuration" page as 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 will override 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.
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4.  "Gateway Configuration" page.

Go to the Gateway and select the PRI that you are using for outgoing calls. Under 'Outbound Calls' you should see the Caller ID DN field. In here you can configure also the Caller ID.
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In other words Caller ID works as follows:

1. Gateway configuration overrides everything else.
2. Route List configuration overrides the Route Pattern and the Directory Number Configuration.
3. Route Pattern overrides only the Directory Number configuration.