i would imagine they wouldn't need GPS if they can get a court order to access (or if they already have access by other means) to the cell network; i've read the other day that thing in movies and TV where they need to wait for a call to happen and last for a given time is ********, it's just to add suspense or help with the plot, in real life tracing a number is pretty much instantaneous, in some cases it doesn't even need a call to be done