It could also be done using (M-AG's) phone-control program. build a simple script for the dial or sms.

Phone-Control is a great program/script/thingy! could be used for this!!

Also, it would not be easy to judge the "fall".
i would use this program for trail bike riding (bush). how could this distiguish a crash/fall or a jump/steep drop?
I don't think it could.

it would be more efficient if you just make a big black back ground and a huge red button on your screen to press to sms/dial a number...

maybe add an external big red button?? use a gamepad kind of setup to push the button which hit the keyboard buttons...