Semi-offtopic: my life has gotten a little bit better since I used the Android (other OSes likely have similar functionality) option to block any witheld or blocked caller IDs.

Partly because it's rarely anything good these days if it's a witheld number, but mainly because my workplace's outbound calls get automatically blocked so work calls don't get displayed on my phone unless someone uses Skype or a work mobile. Winner.

9/10 would recommend A+++++ unless you're on call, of course.