Why not take an old cell phone (be it Android, iOS, Windows Mobile, or Windows Phone 7 based) and build an app on top of that)?

More so... is a 24/7 always on display (what I am assuming you are looking for from such a panel) really needed?

You could probably do this pretty easily with just a Netduino (or similar embedded controller) which exposes either a web site or api set that is controlled via a PC or mobile device.

... of course you do raise an interesting possibilities with regards to modifying a consumer GPS unit.