We’re stretching credibility to suppose that a cell phone signal can penetrate that far underground. GPS will be a lost cause, and while the phone company will be able to figure out which cell tower you are connecting to, that only narrows it down so far.
People really did/do worry about this. Yes, it’s a thing.
If you are able to leave your preferred burial instructions before you are buried, you can ask for a Safety Coffin with some kind of connection to a bell on the surface that you can ring. These were apparently quite popular in the 18th and 19th centuries, but (sez Wiki) are even still available today.
(Is this option allowed to Jews too? 
)
I suspect they are better at distinguishing who is actually dead today.
& they faint/freak out when they think you’re calling from Beyond.
Serious question - how quickly do they fill in the hole? At every funeral I’ve been to, there’s some ceremonial dirt tossed on top, then everyone chats for a few minutes before heading back to their cars & figuring out where they’re all going. Once the workers come over, they’d need to remove the tent, chairs, astroturf ground covering, etc., which takes a few more minutes. I’ve never seen the workers there gunning the backhoe’s engine trying to move people along so they can finish their day & go home. You’d get, what, an hour (?) before dirt is on top of your casket which would block the cell phone signal.
I work as a supervisor in a 9-1-1 center.
Triangulation of caller’s location happens in a few seconds typically (though carriers have up to 6 minutes to provide location data), assuming you connect to a 9-1-1 answering point that has phase II wireless capability. If your phone cannot send GPS coordinates then this would be the best information to go on. If you are able to tell the 9-1-1 call taker that you are buried then the location given should be within 300 meters, close enough to search pretty quickly to find freshly turned soil.
Some 9-1-1 calls are received with location data available at the time the phone rings. Others we have to click a button on a computer to send a request for the data, known as sending a bid (or re-bid if you have to do it a second time). AT&T states they have phase II location information available for 99% of calls within 30 seconds.
But if the center you connect to only has phase I or Basic E911 then you are pretty much out of luck. The best you could hope for is that they will quickly get which cell tower your call was received from.
It probably varies from place to place, but I was at a funeral about 20 years ago where immediately after the graveside service 3 or 4 of the male relatives grabbed shovels out of their vehicles and filled in the hole. This was at a private family cemetery.
Maybe a real asshole relative? “Quick, everyone, grab a shovel!!”
If this is a more-or-less typical US style burial, your calculations and assumptions need tweaked. The coffin will be inside of a cement vault. The wooden coffin will not seal air and water tight like the more expensive metal ones do, so your calculations of available oxygen should include the interior volume of the vault not the coffin. There will not be six feet of earth on top of the coffin. The grave will be dug about six or seven feet deep, the lower part of the vault placed in the grave, then the coffin, then the upper part of the vault. You end up with three feet to four feet of soil covering the vault. Signals, therefore, need to penetrate the wooden coffin, a couple inches of cement and three or four feet of soil.
Amateur radio operator here, radio signals typically travel through solid objects about as well as light does (both are, of course, non-ionizing radiation waves, so this makes sense). Higher-frequency signals such as UHF, Wi-Fi, or those used by mobile and cordless phones tend to be better at penetrating through things like structural materials, but yeah, six feet of earth could be a problem even before things like concrete vaults and coffins concealed inside of Faraday cages.
I actually hadn’t considered whether cell phone towers are set up to focus their signals on the horizontal plane rather than being omnidirectional, but it would make sense given that relatively few of the phones those towers need to connect with will be above or below the horizontal plane. If you’re curious, you can do this by stacking two directional antennae vertically. It causes increased gain on the horizontal and reduced gain on the vertical, due to how radio waves interact with each other (shorter explanation: it’s magic, I’m still studying for my General license and only understand that it works that way, not why it works that way)
To clarify something, by “more expensive metal ones” I meant that higher priced metal coffins offer features like being air and water tight that cheaper metal units do not. Wooden coffins, depending on materials and finish, can be breathtakingly expensive, but it isn’t possible to seal a wooden container as tightly as a metal container.
I haven’t any factual to add, but if the OP haven’t seen Buried, it offers a movie-long exploration of more or less the scenario descriped.
I’m thinking coffins are pretty standardly sized. So your range of movement probably depends on how big a person you are. A skinny person will have a lot more wiggle-room (so to speak) than a portly one.
No doubt. But it does still happen. Here’s Snopes on the subject. You still see occasional reports of this happening (though not of people being buried - just people waking up in hospital morgues after being declared dead).
They buried Jaime in a metal casket in Mythbusters Season 1 Episode 5. They called it off after 30 minutes, the metal lid started bending from the weight. Between the build up of temperature and CO2, and the decrease in O2, well, it’s not a great situation to be in.
kayaker:
Or Jewish ones. Burial of the dead is considered a kindness to his or her soul, and pretty much everyone at the grave site (except the most immediate mourners) shovels in some of the dirt in order to do some portion of said kindness. That also gets back to a question asked earlier upthread about how quickly the hole is filled in after the ceremony is over, for Jewish funerals, it’s immediately.