I got a reply from CC from my ticket.
Hello,
Yes, while we can "force" your outbound caller ID to be xxxxxxxxxxx, please note that given if you do call 911 emergency services, emergency services will not see this caller ID, rather they will see a "hidden" number (that is associated under your account) as the caller ID. Just to explain how we've implemented 911, for every client that has at least one paid service and has stated that they will be using our services within the US/Canada, will have a 'hidden' phone number associated under their account (this is just in the event that if you ONLY have an outbound service under your account, you can still receive inbound calls from the emergency service center). Please note that you will not be able to receive regular inbound calls through this hidden phone number; this phone number is only accessible given if you have dialed 911 and the call happens to disconnect abruptly; emergency services has a means of contacting you back. So when you do call 911, emergency services should see the hidden phone number as your caller ID.
If you have any other questions, please let us know.