I have been getting nuisance marketing calls etc lately on my mobile phone which is getting to be a right pain in the backside! Sometimes I don't answer my phone and later look up the numbers on the Internet, these usually lead to forums with people complaining of calls from exactly the same numbers, sometimes there is no one on the other end of the phone if you do answer.
Up until now, I have saved these numbers in the contacts list on my iPhone 5 as "CRAP CALL" and just cut them off when they ring again or just don't answer the phone.
However, If you have an iPhone then there is a method of blocking the call. What actually happens is that the number ringing you will be continually diverted to your answerphone without your phone ringing. Most nuisance / marketing calls won't bother leaving a message as they know you won't be ringing them back.
This is how to do it on an iPhone and it's simpler than it sounds as it only takes a few seconds....you can unblock calls if you have blocked a number by mistake also by this method.
Go to the green phone app symbol and click on it.
Then look at the very bottom of the screen and click on the clock face symbol, entitled "recents",
This gives you a list of all your recent incoming and out going calls.
Find the number you want to block and press the circular information symbol on the right
This opens up an information page, simply scroll down and press "Block this caller".
Phones other than IPhones may have a similar method of blocking which you could look up on the net.
Hope this helps.