My preferred carrier is not on the drop-down list under the Port Out tab. Can I still port my number out to them?

In this article:

Hey, why is the service provider you want to use not on our list of possible carriers to port out to?

Good news: The list of possible port-out carriers just includes the most common carriers we've worked with in the past. The truth is your porting credentials remain the same regardless of which carrier you're porting your number to. But when we didn't have a list, people got confused.
 
As long as Cox Business can support the rate center for your number (Why are rate centers important?), you can port your number to them by following the instructions in this article:
 
Step by Step Guide: How to port a number away