The problem here is that once you give out a number then it's public in some sense. The person you give it to can pass it on, even inadvertently. The smart thing to do is to have a public number and a private number. It makes no sense to call cabs with the same number you use to contact sources or whatever. This is easily done with dual sim phones and can be taken much further with Google Voice or other dial-in phone…
> The smart thing to do is to have a public number and a private number. What's the easiest way to do this?
(or a double SIM phone, but then you still risk messing up yourself by mixing data / calling from the wrong number / etc)