was my understanding. I have a full Gigaset set up with three different VoIP providers ( there was a fourth too) plus PSTN. All new(ish ) handsets work fine and even older BT branded (various manufacturers) work with with it. PSTN is moving to BTs Cloud Voice (contractual reasons) and they supply a pre-provisioned Yealink. With info from here and elsewhere, I will not get the SIP details for BT to programme into the Gigaset - a real pain, and the Yealink does not support Gigaset handsets.
Seems as though some manufacturers build in incompatibility.
M H C
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