use this configurations
default]
exten => _1NXXNXXXXXX,1,SetCallerID(your callid number|a)
exten => _1NXXNXXXXXX,2,Dial,SIP/${EXTEN}@gafachi
exten => _1NXXNXXXXXX,3,Hangup
exten => _011.,1,SetCallerID(your callid number|a)
exten => _011.,2,Dial,SIP/${EXTEN}@gafachi
exten => _011.,3,Hangup
change where says your callid number with the 10 digits of you call id number