Arsenijs from Latvia has created the ZeroPhone, and he reckons it has only cost around $50 to build! It can be used for making calls, sending SMS messages and has various text-based mini-apps pre-loaded. It runs Raspbian and pyLCI for the UI elements. The bill-of-materials is as follows:
- Pi Zero – easy to get despite people on Internet still telling otherwise (I got 5 by now). Let’s say it’s 5$ and 5$ for shipping.
- SIM800 modules – available in large quantities from eBay, 5$.
- ESP8266-12E used for WiFi (as per RPi-WiFi project) – 2$ from eBay
- Two-layer PCBs (two 4x10cm boards, one 4x6cm board) – can be ordered from your favourite fab or whatever people on Internet give good reviews about.
- ATMega328P – can be desoldered from an Arduino Pro Mini that’s typically 2$ on eBay, and it comes with a bootloader already! If you don’t have a heat gun, you can just buy a bare chip and burn a bootloader to it using a programmer.
- LCD screen – 5$ on eBay. Besides, a project like this can use other screen breakouts with similar characteristics (such as the ubiquitous Nokia displays) – it’s just a matter of writing a driver, which is easier than it sounds, and the front board accepts different display pinouts.
- Battery – you can use cell phone batteries, pouch and 18650 cells.
- TP4056 battery charger – modules are available from eBay, 1$.
- Buttons for keypad – 2$ from eBay (there are 3 types used, but you can omit one).
- 2.54 headers (both dual-row and single-row) – dirt cheap. Won’t be more than 0.50$ to have enough to assemble the phone.
It’s currently at working prototype stage and is, basically, a Pi Zero sandwiched between circuit boards. You can read more over on Hackaday.io.