We have Swyx DECT 500 Base Stations and some Swyx Handsets.

As I know the DECT 500 is a branded M700 and the Handsets are M85.

We bought some original M85 and could Register one Handset and when registering the Second Multicells reboot and the Handset is unregistered.

So I need to upgrade from 3.xx to the latest Firmware. We switched the PBX Vendor and the old Partner never upgraded the Firmware of the devices and would not upgrade it anymore. 

Is it possible to upgrade with the original Snom Firmware Versions?