I built a simple touch screen phone battery powered (optional solar)

TL;DR: With parts I already had (everything besides the LTE module) I built this touch screen phone with basic features such as receiving calls, making calls, sending sms, receive sms, contact storage, settings (4 languages, english, german, romanian and croatian), signal strength indicator and toggleable clock. It runs on a Raspberry Pi Zero 2W and can be solar powered (I just need to connect my solar panel to the Solar Power Manager).

Component list:

• Raspberry Pi Zero 2W (Raspbian installed)
• A7670E LTE Cat-1 HAT (with LBS)
• U.FL Antenna
• Solar Power Manager Module (D)
• Battery Tray
• 3x18650 Batteries
• ILI9488 3,5" Touch Display (I took from another project of mine)
• USB-A-to-C Adapter
• An old headset from a Nokia phone with 3.5mm jack (to make and receive phone calls)

For the screen I use ili9488_adafruit.py library. For the LTE module I use serial library and AT commands. For the screen and touch controller I use two SPI busses because I didn't want to use a breadboard to wire them to the Raspberry.

Some tips: There can be XPT2046 or HR2046 (it's a copy of XPT) touch screen controller on your ILI9488 3,5" display. Use a small self-written gpio wrapper class to use ili9488_adafruit.py if you run into display issues. Calibrate your touch screen with a helper script and update your touchscreen logic according to your measurements. Disable bluetooth and enable SPI1 in config.txt, also free up the serial port and add the user who executes python entry script to group dialout.

I've also used the A7670E LTE Cat-1 HAT in another project with an ESP and well it can act as a modem if initialized as a modem and if you use it directly with AT commands, you can make direct https calls if you need to (this can be very useful) and much more. It's also a pretty cheap LTE module about 39$.