I would not depend upon the GPS feature in your cell phone in providing an actuate coordinates for potential rescue. We had a rescue early this year and were planning on hoisting the patient out using the Maryland State Police Trooper 3 helicopter for the operation.

Before heading out up the trail, we planned on taking our two GPS units, unfortunately someone had left alkaline batteries in both units, in addition to units being dead, the batteries had leak, making them unusable. We hiked to the patient, planning on providing landmark details to the TRP3, since there was considerable canopy coverage and we knew it would be hard for them to see us on the trail or even in a nearby clearing.

One of our members had his cell phone and called the Emergency Communication Center (ECC) to relay GPS coordinates to the helicopter. Despite plugging the indicated coordinates into their navigation system, they were at least 5 miles from our location. After numerous attempts to guide them into us over the radio, they were able to locate us and performed the hoist operation successfully.

We debriefed with them later and they said there was considerable difference between the cell phone GPS coordinates and their navigational GPS coordinates, determined once they visibly located us.

Just FYI.
Pete