Sometimes, even with all the modern gadgets, you can find in use, stuff gets lost.
This time, 5 people in the US had a plan of setting off a weather balloon equipped with a GoPro camera and a mobile phone. They planned it so that the balloon would drop back to earth and send a message to them with the GPS location of the crash site. It turns out the location the balloon crashed had no cell coverage as was suggested on maps they used. So, with 100's of square kilometers the balloon could be, they assumed the balloon lost and the footage taken by the GoPro as well.
Skipping 2 years, a woman, working at AT&T (the phone provider the guys used) was hiking trough the dessert found a phone and took it to an ATT shop to find out who's phone it was, and they traced it back to the owner, and he got it back a bit later. I assume the GPC coordinates were still on the phone and they used that to located the crashed balloon to, after 2 years, get the lost footage.
Below is the message the guy posted on Reddit:
The whole project took myself and four friends a couple months of planning. We almost canceled the whole thing because helium cost 4x more than we were budgeting. As for the communications and attempted recovery (warning, about to get technical):
We used GPS on a smartphone to continuously log the phone's location on its memory card. The standard GPS receiver these days can track your phone well above 100,000 ft - there used to be a limitation of 60,000 ft, but that was recently lifted. The harder issue was to figure out how the phone can communicate to us. We used an app (myTracks or something similar, I forgot) to have the phone text us it's GPS location once it got a signal as it was returning to Earth (about ~3000 ft altitudes).
We planned our June 2013 launch at a specific time and place such that the phone was projected to land in an area with cell coverage. The problem was that the cell service coverage maps we were relying on were not accurate, so the phone never got a signal as it came back to Earth, and we never heard from it. We didn't know this was the problem at the time - we thought our trajectory model was far off and it landed in a signal dead zone (turns out the model was actually quite accurate). The phone landed ~50 miles away from the launch point, from what I recall. It's a really far distance considering there's hardly any roads over there!
TWO YEARS LATER, in a twist of ironic fate, a woman who works at AT&T was on a hike one day and spotted our phone in the barren desert. She brings it to an AT&T store, and they identify my friend's SIM card. We got the footage and data a few weeks later!
And of course the lost and then found media: