... on very many variables.

I have been giggling many times when Jerry Bruckheimer has invented a way to locate a cellular phone within 10 metres. This is not possible - especially not in a city where there are many reflecting surfaces and no way for the radio signals to have a straight route.

There is a compensation system in GSM protocol which tells the approximate length of the radio signal path. There is no way of telling which route it has taken and therefore the triangle measurement will give incorrect results. In a city environment the best accuracy of GSM positioning is measured in hundreds of meters - not in meters.

The situation is way better on open landscape. In desert (or sea) the accuracy can be somewhere in the vicinity of 50 metres. This however requires that there are at least three GSM sites on different masts in the reach of the phone. This not true most of the time as the operators want to build coverage - not capacity on non urban areas.

The only real positioning system is to integrate the cellular with GPS system so the base station can ask the position.