Should you wish to override the default outbound Caller IDs, which are automatically set to your company name or number, you can do so through Portal. Login to portal, then select the Settings tab, followed by Default addresses and numbers.
If you're changing these setting for one of your customers, you will need to become them first by using the Switch User button at the top of the page.
You can set the following:
Default fax caller ID: This is the default phone number shown as the From: on the receiving side
Default fax station name: This is the default 'Company Name', shown as the From: on the receiving side, and can be text or a number. This may not be supported by all fax machines.
Default SMS caller ID: This is the default From: shown on the receiving mobile phone. This can be a mobile number (if you have a 2-way SMS product), or a text string up to 10 characters.
Default Auto Call caller ID: This is the from: number that is shown on the receiving phone, when placing a text to speech call through communicator or the API.
Once you have set the fields appropriately, click Save Defaults.