Here in the USA that no call list is almost worthless. I sit at family members' homes and just shrug as one call after the other comes in from various 800 numbers. Its laughable really, because they feel the need to answer a ringing call. I don't get it. I only have cell and no landlines anymore. My phone only rings for numbers in my address book. Quiet and nice. Although I get a ton of calls, its from those I know.
I only have a cell phone for out going calls only and I have my caller ID off. On if a call back is necessary or I want them to have my number for future contact. I think it is possible for people to figure out your number if they really want it bad enough.
Even though they are not supposed to, I am almost certain my banks, credit card companies, and the like are "leaking" my contact information. You define "leaking" any way you want.