In writing the previous entry, another idea came to me that I stuck at the end which is worthy of its own entry. Place an accelerometer in your cell phone that will detect a violent event, such as a car crash or bike crash. Similar to the detector already in the car that triggers the airbag.
Upon detection of the event, the phone would start beeping for about 30 seconds warning about the emergency. If there is no emergency, you would press any key to stop the call. Otherwise it could call 911.
However, it would need to be sure not to trigger an emergency just because you dropped the phone or threw it or went flying when you turned a corner in your car. However, if this can be arranged it could be a handy feature to sell as a cell phone extra.