As usual, GPS and cell died while hiking last weekend. I plugged the phone into a charger at home and it remained hot with no signal until I rebooted. It turns out that this is easy to reproduce. Wrap up the phone in two layers of aluminum foil like a burrito, let it sit for a while, then take it out. It continues to malfunction after being unwrapped - no service or roaming without data. I also noticed that it periodically jammed 5GHz WiFi while wrapped up. The phone's WiFi was turned off so it shouldn't have been on that frequency.
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Sprint stores won't repair it because I refuse to pay extra repair fees for a phone that is defective under warranty. I sent it to Samsung for warranty repairs three times without any improvement. The last time it came back from Samsung it had a firmware update that disabled GPS and caused the cell signal to flicker on and off. I attempted to get a refund from a Sprint store but they were able to restore the factory firmware.
GPS and cell reception has never worked reliably. GPS occasionally works in an open area after restarting. Cell reception is weak - it doesn't work where Sprint's coverage maps say it should. Driving through or hiking in areas with no coverage causes the phone to become warm and malfunction.