> but cell tower data isn't going to be as accurate as GPS

My knowledge in this topic is not deep, but cell precision should be pretty accurate, because modern cell tower areas are much smaller, then to have well tuned beamformer it need to have relative precise angles between antennas and know signal travel time (distance). I think it should achieve something 30 or 15 meter precision (doing assumption that distance is accurate in 50/100ns order)