I currently receive a large number of spam calls, accident claims, automated PPI calls, mobile phone marketing calls etc..
I am still running iOS 6 on my iPhone, if you have upgraded to iOS 7, this is a lot easier, just go to the phone app at the bottom of your home screen, open it, look for ‘recents’, simply click ‘i’ next to the number you want to block, scroll to the bottom of the next back and click on “Block this caller”.
For those of you not on iOS 7 or in fact on any phone, this is my method. It doesn’t block them, but it ensures you can red button them for eternity!
Just create a spam contact, add them. Done..!