Alcatel Unleashed

Hello guys! Heaving a hard time with system here. I have a need to register Handheld phone to a subscriber that never had it before. Now I know how to do a Gap registration, but the subscriber of interest don’t appear in the list. If I choose the number I want in Subscribers/basestations list it has a status of “Single-line” number. Is it possible to modify it? Or am I doing it all wrong there is another procedure of adding handset to an existing number with stationary phone?