I bought this phone on a antique market somewhere and kind of fell in love with the heavy feel of the number dial pad (and the rest actually; the speaker alone has the same weight as a mobile phone).

RTT Phone

ah… the craftmanship… I pulled the guts and am planning on inserting my girlfriend’s old Siemens SL55. I want to use a PIC in order to decode the dial pulses and send it to the serial port in the Siemens mobile. Would be nice to also trigger the old bell circuit inside the phone but this would require extra batteries. Not sure if I want that. By just using the Siemens phone and the PIC I can use it’s own charger. The RTT even has a handy brace on it so you can walk around with it and use it as a real mobile phone!