You wouldn't do anything.

VoIP providers including us aren't involved with porting out at all. When someone ports a number out, we're rarely even notified. Our policy with our customers is that they must contact us to cancel their account in order for it to be canceled. We don't automatically cancel it on port out since we aren't involved/don't know about them.

Porting out is all handled by the underlying/upstream carrier that the phone number is issued to us by.