CID from SIP into master.csv. How_to?

Hi,

I have a GSM-Gateway device connected to my *, via SIP.
Everything works fine, however, in master.csv I only get entries with src “GSM-Gateway” (name of the device in extenions.conf), when somebody calls into the GSM-Gateway using a mobile phone.
Of course, I want to have the real CID.
Any idea, how to achieve it ?