Finally, an adapter connected to the FRITZ! Fon MT-F is working and one a 'normal' PC headband headset with 3.5 inches can thus operate jacks. I find these small in-ear mobile phone headset that will probably also work with the Fritz! Fon, fiddly as unpleasant and. Therefore, I use the adapter together with a Plantronics Audio 310 Monaural PC Headset with Microphone. No hum, no echo, no complaints of my interlocutors. And all together for less than 20 euros! 5 Stars!
