cant make a call to friends because my phone has witheld no feature on it ?

Hi what i would like to know is ,can i put a no code before dialing my friends no so it unwitholds my no so i can ring my friend.because at the moment i cant call my friend because his phone wont accept calls from witheld nos.is there one for setting witheld and one for unresetting .im with bt.
many thanks .paul.

paul.
June 2010