Quantity   Component name
1 × Vintage rotary phone in working condition I used the L.M. Ericsson Dialog
1 × Arduino Pro Mini, ATmega328 Using the 16MHz version with the 3.9V from battery directly to VCC seems to work fine
1 × QCX601 SLIC module Using other modules would probably require changes to code, but nothing major
1 × SIM800 or SIM900 series breakout board, mini version Make sure it's got breakouts for mic and speaker
1 × Li-ion charger board for 18650 battery The kind with power output
1 × 18650 Li-ion rechargable battery, 3.7V Mine says 9900mAh, but I'm guessing it's more like 2500mAh
1 × Battery holder for 18650
1 × Slide switch, DPDT For power on/off, to be mounted through bottom plate
1 × 3.5 mm barrel jack female Unless you want to use the micro USB port on the charger board
1 × 3.5 mm barrel plug cable to USB A Or micro USB cable to USB A if you want that instead
1 × USB power adapter/charger For.. you know.. charging...
10 × Connection wires With and without Dupont connectors (AWG24 for power connections)
1 × Capacitor, electrolyte, 470uF 16V Place close to SLIC board, between VCC and GND, mind orientation
1 × Capacitor, ceramic, 100nF 50V Place close to SLIC board, between VCC and GND
2 × 3.5mm TRS male Only if your GSM board has got audio jack connectors
1 × Perf board Experiment board to keep all the things in place
1 × Socket, 24 pin wide DIP For the Arduino Pro Mini
1 × FTDI programmer USB to TTL serial converter
1 × SIM card With PIN code disabled