Re: What can a user do ? Use multiple devices ?
Lots of people have multiple devices e.g. "work" phone and "personal" phone (typically with different SIMs)
Employer has number of your "work" phone which you have turned on when not in the office or when on call. i.e. you control when that number is available based on work needs (similarly if self employed, customers have this phone number)
Your "personal" phone number NOT given to employer, but is used by friends and family to contact you.