buy a 20.00 burner phone from 7-11 and port your number into it, use the web account or phone options to set up your forwards. Put the phone in a drawer and shut it off. It should last years if not too many people call it.
... but you should be able to make outgoing calls from that number from time to time, too.
Yes, of course, it's a basic cell phone still. Many buy them, drop 20 bucks on it, pull it apart and make a nice GPS tracker insead of paying $800 for a "professional" work truck positional monitoring system.