A modern android cell phone has a camera, screen, light, keyboard, speakers, battery, and a cpu that is many times faster than the z80 counterpart and all the software to go with it. There are also various short range communication and mesh networking abilities (NFC /Bluetooth/WIFI). Its not too difficult to create a wifi router out of a phone. You can purchase many USB to GPIO boards cheaply online (as a pepper your stock piling stuff anyway, your not going to just find a z80 laying around either, there are even adapters for ham radios you can pick up cheaply). I could easily see using a camera network from cell phone for proximity alerting, mesh networking of a few city blocks to create a communications network and basic note taking and information storage fitting into a few phones storage, in addition to having a fully functional Linux machine. I'd wager that if you take all the time it takes to create this project and compare its success to the time it takes to buy 30 GPIO adapters, download the rootkit library for android and some cables, that you'd have more success going with the phones. Also, just think about moving around... a backpack of cell phones isn't going to have the failure rate that you'll get with exposed electronics.