sbiddle: Regular corded or cordless handsets work fine with both Genius Lite and Genius. They both have RJ11 ports on the back to plug in any analogue phone.

You can also attempt to pair any DECT phone with GAP support to Genius as it has a built in DECT base station.

There is no need for the Genius phone to use the phone capabilities.

it also passes through callerid if your third party handset supports it.