Hello everybody,
I stuck one week ago with this issue.
I have register one phone with number 500, I want this phone when makes outbound calls to have translated number of 4923407 for example.
I know this thing is simple, but i;ve stuck on it 
.
Here is some config, extension.conf:
[globals]
ICONNECT1 = 91906
ICONNECT2 = 492340
ICONNECT3 = 500
[general]
static = yes
writeprotect = no
[default]
exten => s,1,Verbose(1|Unrouted call handler)
exten => s,n,Answer()
exten => s,n,Wait(1)
exten => s,n,Playback(tt-weasels)
exten => s,n,Hangup()
[incoming_calls]
exten => _X.,1,Dial(sip/${EXTEN})
;exten => _9028169XXX,1,Dial(sip/${EXTEN})
[outgoing_calls]
exten => _X,1,SetCallerID(${ICONNECT2})
exten => _X.,1,Dial(SIP/my_service_provider/${EXTEN})
exten => _X,2,SetCalleID(${ICONNECT1})
exten => _X.,2,Dial(SIP/destSTZ/${EXTEN})
[size=150]exten => _X,6,Set(CALLERID(num)=4923407)
exten => _X.,6,Dial(SIP/+${EXTEN}@my_service_provider)[/size]
[internal]
exten => 4923407,1,Verbose(1|Extension 4923407)
exten => 4923407,n,Dial(SIP/4923407,30)
exten => 4923407,n,Hangup()
exten => 500,1,Verbose(1|Extension 500)
exten => 500,n,Dial(SIP/500,30)
exten => 500,n,Hangup()