Caller_ID

Hi there,
i’m new member Peter with an asterisk installation and i want to have 10 ip-phones.

My problem:
i would like to have always the same ID number for outgoing calls, no matter which phone is calling out.

does anyone know a smart idea?
i tried it on the sip-trunk, the outbound rule and the phone, but it doesn’t work.
If i make an extension it is working for inside and outside calls.

Peter