Receiving JSON Data via HTTP POST with PHP

If you happen to follow my blog you know that I’ve been working on this new app called WingsuitGP (Air Races Powered by iPhone). Yesterday while working on the app I found myself a little stumped having to do something I’ve never done before… how do I receive JSON data via HTTP POST with PHP?
In the past I’ve used PHP many times to spit out JSON data back to a web or mobile app. But with WingsuitGP I’m having to do the opposite. The mobile app is the one spitting out the JSON, and the backend PHP script is on the receiving end of these data. So I just wanted to sort of bookmark this cool blog post I found from on how to go about doing this: Receiving JSON POST data via PHP
I found another excellent post on Receive JSON POST with PHP
Also, here is an example demonstrating how to send JSON data via HTTP POST using client-side JavaScript: What is the way to send a JSON object via a POST request in JavaScript (not jQuery or Nodejs)?