setting outgoing calller id private per extension

its all going to have to be manual for you.. and if you are someone who buys service from a half-dozen different providers then its probably not going to work for you at all. There is no 'one way' of masking the callerid and different providers expect different methods to comply with their equipment. If you had only a single provider for call termination then it would be possible, only after you made all neccessary customized dialplan entries. If you have multiple providers then you can just about forget it since its highly unlikely they all want it done the exact same way.

Thanks Erik. We do have just one provider so that shouldnt be a problem. Do you have any directions or link what and where things have to be changed ?

that depends entirely of the method invoked.. I like providers that accept Remote-PartyID because thats a simple 1-line modification

SetCallerPres(prohib_passed_screen)

you can even make a fuction for something like *67XX. that will strip the first 3 digits, set this value, then deliver the rest of the number to your regular outbound dialing patters.

Actually, that method is deprecated. What I found out was the Asterisk cmd CallingPres() is deprecated in favor of SetCallerPres(), the Asterisk cmd SetCallerPres() is deprecated in favor of Set(CALLERPRES()=allowed), and the Asterisk cmd CALLERPRES() is deprecated in favor of CALLERID(num-pres) and CALLERID(name-pres). (Does anyone see a pattern here?)
According to the Asterisk 1.8 documentation, the following datatypes have all been dumped into the CallerID function:

Syntax

CALLERID(datatype[,CID])

Arguments

datatype - The allowable datatypes are:
all
name
name-valid
name-charset
name-pres
num
num-valid
num-plan
num-pres
subaddr
subaddr-valid
subaddr-type
subaddr-odd
tag
ANI-all
ANI-name
ANI-name-valid
ANI-name-charset
ANI-name-pres
ANI-num
ANI-num-valid
ANI-num-plan
ANI-num-pres
ANI-tag
RDNIS
DNID
dnid-num-plan
dnid-subaddr
dnid-subaddr-valid
dnid-subaddr-type
dnid-subaddr-odd
CID - Optional Caller*ID to parse instead of using the Caller*ID from the channel. This parameter is only optional when reading the Caller*ID.

depreciated doesn't mean non working. We will never support asterisk 1.10 .. we will be sticking with 1.8 until the next LTS release comes out. This command works in 1.8 which will be the version thirdlane uses for the next 2 years.