I have idea of using cheap android phone on the plane. If attach simple bluetooth<>serial module to Ardupilot telemetry port, Android phone will be able to conect to it. Then special software on phone (had to be developed) will connect through bluetooth to ardupilot, in same time it will create TCP socket to computer on the ground (equiped with mobile data modem) and bridge those conections together. Finally there will be a TCP/virtual serial port software on PC (already available, eg from Lantronix). Better see the picture. Of course, you need two data plan sim cards, but I have them.
As I can't use Xbee (not 900Mhz nor 2,4Ghz) this would be my only chance.
I know that is over-engineered and here are tens of minuses, but phone onboard can do photographing, and in case of crash, there would be chance phone will continue to work. Most today androids have GPS and there is plenty of Locate my phone softwares.
I asked my friend to write such software, if he succeed I will share results.
We've already released an Android interface board (officially supported by Google) to do this. It's here.
I know about this board, but is it supported by current version of APM software? It is also pretty expensive and big. And from my experience of charging android phone with microUSB cable on motorcycle (in cradle on handlebars) this connection is pretty weak and unreliable. It's not way to go for me