Does your phone ring then as you pick it up there's just silence.
Or how do you get rid of sales people in an instant you tell them ....
Sign up to the Telephone Preference Service - that'll get rid of 90% of irritating sales people.
However I did experience having 4 phone calls one day and the number didn't receive return callers.
I put my private eye hat on and discovered it was a call centre based in Southern Sudan.
The crafty solution.
If you find the person talking on the phone is an unwanted caller just say
'You do realise I'm with the Telephone Preference Service and if you do want to carry on with this conversation I do charge £10 a minute'.
It takes then 2 seconds to register what you've said before disconnecting - excellent result. Obviously the indian call centre don't know I'm bluffing but they are not prepared to take the risk.