[War_tijn]

As far as I know they can only see to which tower your phone is connected, so it's not too accurate.

I'm not an expert in this field though.

[chatmasta]

If you repeatedly triangulate a phone at < 100m resolution for a few hours, it should become trivial to identify its exact location. The more people in the area, the less reliable the method is. But in rural or suburban areas, it's going to be pretty good.

See the LocationSmart stories the past few days for more on this.

[adrianN]

When I was playing around with that about ten years ago you could triangulate the position using multiple towers to narrow it down to a radius of a few dozen meters. It depends of course on the density of towers around the phone.