Can I port in a number that I don't own?

In this article:

You want to know if you can port in a number that you don't currently own. The answer is, Yes, provided that it's agreed upon that you will be taking over the number as part of the porting process. We are extremely vigilant to ensure that all numbers ported to our service are properly authorized to do so.

That said, to port the number in, you can follow the process as follows:

Step-by-Step Guide: How to port in a number

You will need to have the current owner of the number complete the letter of authorization and provide a copy of their telephone bill dated in the last 30 days and we will be sure to submit the port request to their current carrier using that information.