Hi tully2021,
Thanks for posting and welcome to our community 🙂
Sorry for any confusion over your additional line query.
You can have two separate lines with different numbers in the same household.
As it's been mentioned the number you're wanting to bring over to us would need to remain active with the current provider so we can port this over to us.
If you'd like me to help with this let me know and I'll pop you over a private message.
Alex_Rm