How to set your Mobile number as unreachable manually

When we don’t want to receive a call we can just block it,reject it ,not answer it ,or switch off the phone
But all these  Methods let the caller that we are willingly not receiving his call

With this trick you can set your mobile number as unreachable whenever you want ,
To begin
Just goto settings-network settings
And click on manual network you phone will search for available networks choose any operator probably the last one
Now you phone will loose all its signal and Now if any one calls you He’ll hear an.unreachable msg
To get signal back ,go back to network settings and choose automatic network