Great question. I would reach out to Visible via their social media channels & ask them.
If they can't, consider porting the number to Google Voice, get a new number on Visible, and forward calls from Voice to the Visible number.
If you don't have a referral code, I would appreciate if you would use mine: Check out this page: https://www.visible.com/get/36mt7h , it has all the info you need to know about joining Visible. When you use my friend code, 36mt7h, you’ll get your first month of service for only $5!
Here are some other tips to save money with Visible: https://community.visible.com/t5/Savings-Spot/5-for-your-your-first-month-of-service-plus-you-could-...