> You'd then be physically nowhere near where the cell tower thinks you are This wouldn't work with TDM networks (like GSM). The cellphone periodically has to

> You'd then be physically nowhere near where the cell tower thinks you are This wouldn't work with TDM networks (like GSM). The cellphone periodically has to produce a timing advance offset, so that the phone can send the signals ahead of its time slot, to arrive at the tower when its time-slot is active. So effectively, your phone measures light-path distance between the tower and your phone periodically, with the help of the tower (this happens in 1/2 km steps). This however isn't triangulation, so all my attempts to use TA + tower location to make a fake GPS (way back in 2004) ended up giving me erratic movements as I went up and down (and behind buildings). Faking Timing Advance would be near impossible, because it uses light speed (on the given day's humidity etc).