when we place a call to a mobile number i would like to know how to identify that for ex ;
- number is invalid / number is busy / call is transfered to mail box ?
thanks for your help 
That will depend on the all the networks between you and the destination, but, if it can be done at all, it will result in the setting of a variable called hangupcause: http://www.voip-info.org/wiki/view/Asterisk+variable+hangupcause