Basic functioning of this project:
This phone can call, cut and pickup voice calls.
More about this project:
Initially, I used the sim900 mini modem. This was easy to connect and it worked well with the arduino nano as it only required a 5V power supply. However, it did not contain any speaker or microphone pins. So, for attaching a speaker and microphone I used the sim800A module. The sim800A module required a 12V power supply.
At first, I used the 0.96 inch OLED 128X64 display. However, I needed a smaller screen. So, I opted for the 0.91 inch OLED 128X32 display for my final model and used it to display the call status and phone number.
Finally, while soldering the model onto a perfboard I reduced the number of buttons used to 4. The final model of the phone contains a speed dial option where the phone can store 2 phone numbers and call them with a push of a button.