Currently sitting on the latest firmware 18.104.22.168 and have not have luck since 22.214.171.124 with either Plantronics CS540 or the Jabra, despite it showing on Snoms website as a working compatible combination.
Talking, hearing - fine.
Hanging up calls - not working. Buttons dont do anything.
I have seen this happening in the past when the cable connection was not correct. Please note that you need two cable connections: one for audio and one for control (via EHS).
Have a look here and make sure you are doing the right connection: http://wiki.snom.com/Accessories/EHS_Advanced#Connecting_to_snom7xx_and_D7xx
I apologize, you are correct. Unfortunately there is no newer build for the 370 as it is EOL.