Problem with cellphone boards is that these do not expose GPIOs and are too often too tightly linked with the rest of the phone (once again our good friend RF comes into play, with some phones e.g. using springs to connect antenna pads with the mainboards, others using antenna cables, others using PCB printed antennas)... and never mind about the custom connectors used for PCB connects which cannot be soldered by hand and due to pin changes can't even be re-used...
Don't expose GPIO directly. Soldering stuff on it can potentially ruin the phone. Have it be connectible to a breakout board and let that board be hackable.
Also let me connect my phone to a monitor and keyboard and use the thing as my development platform. All in one.
Maybe a modular breakout board connectible to the IO port would be a better startup idea.
I've never programmed for mobile devices but are the operating systems open enough to let it be possible to write a drivers for these things?
