I have Yealink T46G and a Sennheiser SD all working great.
I just got my s500 for testing and realized I forgot to buy the Sangoma EHS36 (seriously the same part number as Yealink?).
Before I buy the EHS, I saw this thread Sennheiser EHS "Y cable" and wanted to make sure that the existing Y cord I have will work or if I need a different one.