Hello everyone. I got a bunch of old Nokia 3310 in really good shape, but firmwares need to be flashed ("contact service" message). I know they are 12yo, but can replace easily a Siemens TC-35. By connecting the RX/TX pins of it to the Arduino (level converter 5-3.3v), would it be possible to push the firmware by any way? Some people talk about M-bus, some other about F-bus, i need some clarifications.