Thank you for the reply. My inquiry is not a billing related question, but a TOS one, and I’ve not been able to find an answer. Unfortunately, any time I have contacted customer support with any issue, I’ve found them to be very pleasant, but unable to answer the most basic of questions at times.
Spectrum Mobile TOS:
I don't see this scenario in the terms of service, but it seems to me that if you are the primary account holder and you port out to another service your account would no longer exist. Makes sense to me that the other number would have to be transferred to a brand new account for the other person, probably at whatever the going rate happens to be.
I would still follow the advise from James and call Spectrum Mobile customer service directly. Nobody here is going to be able to give you the definitive answer you're looking for.