Since getting a “modern” mobile phone (a Blackberry Pearl 3G 9105), I realised I was walking around with a configurable interface. That is, a little keyboard, and a display which could, with software, be both output or input (in a sense- I could draw a linear potentiometer, which I would control via the keyboard).
But also, it has comms- WiFi, 3G, and Bluetooth. The latter is particularly of interest to me, because it doesn’t involve any infrastructure, and adaptors to go from Bluetooth to serial are easy to get, and easy to use.
So the combination means being able to remotely (up to around 10-15m) control some microcontroller based device, from a custom, tailored interface that fits in my hand, and is self-powered.