The DIY Cellphone
is a working (albeit basic) cellphone that you can make yourself. It can make and receive phone calls and text messages, store names and phone numbers, display the time, and serve as an alarm clock. It connects to GSM networks (like AT&T and T-Mobile in the U.S.) using a regular (full-size) SIM card. It builds on the hardware and software in the Arduino GSM Shield
but extends it with a full interface, including display, buttons, speaker, microphone, etc. The phone is made up of a custom electronic printed circuit board (PCB), about 60 electronic components, and a laser-cut enclosure. Its hardware and software are open-source and available on GitHub (hardware
Part of my motivation for making the phone -- and helping others to do the same -- is the fact that while cellphones are ubiquitous in our society, most of us have little idea what they're made of or how they work. In fact, you can make a cellphone in much the same way you'd make anything else: find the right parts, figure out how to connect them together, and try to do it in a way that's attractive and robust. Because of the ubiquity of cellphones, there are companies making the components they're made of; with some digging, I was able to find versions of these parts that are possible to buy in small quantities and that are possible to assemble by hand. This wasn't necessarily easy, but it's a very different problem than trying to learn the physics needed to understand how a cellphone tower works.
I've been using various versions of this phone as my primary device for almost a year and have taught workshops in which others have made the phone for themselves. It doesn't require any specific knowledge of electronics, but it does involve configuring software, soldering a lot of small components, and laser-cutting, all of which can be difficult if you haven't done them before. I'd only recommend this project if you already have some experience with Arduino and soldering, or can find someone to help you out. You'll also need to get access to a laser-cutter, or find an alternative way to make the enclosure for the phone.