asterisk users - Jan 2005 - about call out : a strange question.

Hello all,

	I want to use asterisk pbx to give a ring for sip user.when A call B , user B
's mobile will ring.(B always register his sip number and his mobile number
first.)

ignorepat => 9
exten => _9NXXXXXX,1,Dial(Zap/g2/${EXTEN:1})
exten => _9NXXXXXX,2,Congestion

	but I want only let B's mobile ring,B can't access. or when B
access,the phone auto hang up.
what I should do? 
who can told me?

thank you.