It's exclusively my phone number using Cheogram app from F-Droid. I paid for 2 numbers, one number is for bank and credit cards, I use that number to call financial places or verify login. My other number is my personal number and for Molly/Signal, etc.
Since JMP only requires XMPP, a federated service, it's essentially an anonymous phone service, and if you travel internationally, you connect to wi-fi in a different country and can make local calls to anyone back home.
All it is is a VoIP number, and some services detect a VoIP number and require a cell number, but you can port your cell number to JMP, you don't have to have a new number from JMP.
If you pick a JMP number, you can port your JMP to a cell service, and a cell number can be ported to JMP.
I believe, but I may be wrong, that cell/mobile companies get a different batch of numbers from VoIP companies, so if you port a cell number to JMP, it will likely still be believed to be a cell number, but I can't say 100% concerete for sure.