That's just the way phone companies work. If I go to AT&T this morning and cancel my account, that number is gone. I get that Google owning two things that look

That's just the way phone companies work. If I go to AT&T this morning and cancel my account, that number is gone. I get that Google owning two things that look like phone companies could confuse people, but under no circumstances would I ever cancel the service on a number I still needed. And like OP said, I know from my experience that Google almost crossed over into belligerence in trying to tell me the implications of porting my voice number. Even if I didn't understand the technical terms, the sheer urgency of the messaging should give you pause about taking any action lightly.