I read an article on this subject before, now I read another one, stating a little more details.
Two British companies, Hampshire-based Roke Manor Research and the aerospace giant BAe Systems, have developed a system to give an exact location of each cellphone. And with the use of the Doppler effect (distortion of a wave because of the speed of the object that's producing the wave) they can estimate the moving speed of an object.

The system could be used to track traffic jams or to track speeders as they go. The new development has also drawn alot of attention from privacy organizations who are concerned that the privacy of the persons using a cellphone would be intruded when the new system would actually be used.