Seems to me these questions would be better asked at the ATT store rather than here on the TER forum.

Personally, I don't have a secret "hobby phone". I only have a cellphone with Tracfone service that I keep out in plain sight all the time. Since Tracfone numbers get recycled and end up on robocall lists it rings all the time and I simply ignore it if I'm not expecting a call. Everybody else in the house does the same thing. When I use it for hobbying I just clean up all the numbers and/or texts afterwards to make sure nobody sees them but nobody has ever even looked. In my opinion this is better than keeping a secret phone because if your secret phone gets found then you are truly busted.

They sell cutters for that. Worse case it doesn’t work. Then go to Best Buy get a new smart phone pay cash and go. You won’t be able to transfer the old number without registering. Start emailing your favors to tell them ur new number.