Bob Alexander built Blueprintf, a handheld serial monitor with data displayed on a cell phone.
I built a handheld serial monitor to use with my microcontroller-based projects, allowing me to debug them or send them commands from my cell phone or tablet. I can connect it to my project’s UART with two or three wires, then connect via Bluetooth to my cell phone, set the baud rate or auto-detect the rate, and then have one or two-way communication between the phone and the microcontroller. You can see my write-up at http://www.galacticstudios.org/blueprintf/. I’ve also posted the code, schematic, and PCB layout files.