Can mobile phone can be life saving in case of disasters by using the existing technology in it?
You should look up the work of Richard Allen and his group at UC Berkeley. They are working on exactly that.
An earthquake warning system is a system of accelerometers, communication, computers, and alarms that is devised for regional notification of a substantial earthquake while it is in progress. https://en.wikipedia.org/wiki/Earthquake_warning_system
MEMS accelerometer is a relatively very low-cost seismic sensor. This can be placed in any mobile phone. Further reading at: http://seismology.gl.ntu.edu.tw/papers/107_2012_Wu_and_Lin_EEW_book_charpter.pdf
"A MODERN PHONE HAS ALMOST EVERYTHING YOU COULD WANT IN AN EARTHQUAKE SENSOR. THIS CAN BE DONE WITH SMARTPHONES" More details at the below article:
http://www.theverge.com/2015/4/10/8382175/earthquake-early-warning-smartphone-gps-accelerometer
you may look into the published works on Early Warning Systems. Most of the existing systems woks in arrays thus covering a particular region. Final result will be the issue of alarms particularly to the high speed trains particularly in Japan.