Siemens Handsets on W60B?

[mrfokus]

Dear support crew!
I am on the way to take my Hipath/Unify equipment out of order. I have here a Yeastar S20 and a package W60B with W56H for starting and trying. Finally I need 6 fixed extensions and 5 handsets.

My wish was to continue using my existing DECT devices Octophon SL3 professional an several Gigaset S4 professional with the new W60B.

I managed to register them on the base station. Incoming calls are displayed with the extension. Dialing and receiving calls stop at the moment I press the green key. Intercom mode between W56H is working.

Is that a configuration problem or are my handsets technically not compatible with the use of W60B? Would a Siemens IP DECT device (like https://www.gigasetpro.com/en/systems/sy...10-ip-pro/ ) solve my problem?

Thanks for your support!