https://www.cape.co/blog/product-feature-secondary-numbers
I've been using my Google Voice number for something similar. But Cape doesn't specify if/when these numbers are rotated in any way - you have three numbers to track now, and you can't retain these numbers if you switch services.
They are real numbers, not VOIP. That can matter depending on what they are used for and if the entity you are expecting a message from blocks sending to VOIP numbers.
The numbers don't rotate like our identifier rotation. They are yours. You can choose to delete a secondary number in the app, and if you have less than two, create a new one after 30 days.