It's not triangulation, it's multi-lateration and the spatial resolution depends on just how good the basestation clocks are. And they've become very good. Every telco in the USA stores multi-lateration for cell handsets location for 2-5 years by default. They both sell this commercially and provide/sell it to authorities on request.

>Multilateration should not be confused with triangulation, which uses distances or absolute measurements of time-of-flight from three or more sites, or with triangulation, which uses a baseline and at least two angles measured e.g. with receiver antenna diversity and phase comparison.