If you need to register the Konftel 300Wx to an analog Konftel DECT base, you must first set the Konftel DECT base in registration mode. 

This is done by pressing and holding the button on the base for 4 seconds. 

Then you go to the Konftel 300W in to MENU > SETTINGS > DECT > REGISTER and enter 0000 as PIN code and just press enter if you're asked for a PARK code. 

The display will show "Success" after a successful registration.

Video below will show "HowTo#