Outbound call gives unknown caller

No matter if CLID auto match is used or not for Outbound Caller ID in PBXww I always get unknown caller. I am using a Gigaset C610A IP phone. ID on inbound calls works fine. Any ideas what could be wrong?

Are you calling a local number? ( Local to your FlyNumber).

It would work best calling local numbers, not to say it wont work otherwise but worldwide carriers differ.

Just in case its a setting on the Gigaset ( which should work fine ) please try with x-lite to see if you get the same issue