Cell phone tower triangulation and GPS tracking are methods of locating a person using a cell phone. Triangulation by cell tower requires assistance from the phone company, special permission and equipment. GPS location requires a GPS-enabled cell phone and software.
A cell phone's service provider can ping a phone, which gives a general location based on the return signal. Accuracy depends on how many towers are within receiving distance of the phone. The more towers as reference points, the more accurate the location. Accuracy can range from a few hundred feet to several miles depending on the number of towers in range.
GPS location programs are very accurate. They use the GPS feature available on most cell phones. Any phones with corresponding software can immediately locate each other, within a few feet.