[Asterisk-Users] setvar CALLERIDNUM

[Matteo Rancilio]

Is it possible to change the var CALLERIDNUM?
I need to put the 0 in front of the incoming number to be able to make a 
redial on a missing call.
We need the 0 to rich the external line

I tried with
exten => s,1,Answer
exten => s,2,Setvar(CALLERIDNUM=0${CALLERIDNUM})

On console I see the new variable but in reality it does not change the 
callerid number on the phone display.

Any suggestions?