We're currently running version 68.0.28.
There's really only one display involved (the one on the phone, which is calling) and it shouldn't be based on the trunk provider, since it's only for internal calls.
Let me put it like this: employee X wants to redirect all calls to his extension to a different phone, be it a cell phone or a land line, doesn't matter. He uses the redirect feature on the SNOM phone, which then adds the redirection to the extension on the pbx. So far so good, all working as intended. Now employee Y calls employee X and gets redirected. Employee Y will see in his display, the number he is being redirected to, employee X doesn't want his private cell phone number to be visible to colleagues though.
This works fine, if employee X is called from outside the trunk, any phone from outside the trunk will not show the number, to which it is redirected. Only extensions on the same trunk have this problem/feature.
I'm sorry if this is confusing, I've been trying to wrap my head around why this is happening, for 3 days before I asked here