Nerdindustries is a small innovations lab from Hamburg, Germany. They were looking for a novel way for members of their inner circle to be able to call them literally at the touch of a button. Their effort led them to disassemble a cellphone and rewire the components, adding an amplifier (3.5 watt), a delay controller (adjustable via a trimpot, 10 – 15 sec.), speaker, microcphone, on-off switch, LED indicator light and batteries. They describe their device, dubbed The Phone Box, as follows:
As you already might have guessed, we took the Nokia 100 mobile phone and removed the keypad. But before this we have saved our phone number to a speed dial button. In this case we have used the no. 4 button on the keypad. We used this particular key because there is no way you can braze a wire to this board. So we had to fix the conductor with tape and clips. And we have used this phone because its cheap and it combines a microphone plug in as well as a speaker output in its head set connection. The aim of the whole electronic we have build was to operate the phone with only one switch.
You can read their project summary at the Nerdindustries website.
Matt via the contact form.