I "grew up with" PNG Coffee. Not surprising as I was living there at the time.
The Highlands coffee is special in that the soil is volcanic (lots of volcanoes along the central cordillera 15,000 years ago) but is well-washed by the constant rains. There is little to no sulphur in the soil, which means that garlic grown there doesn't give you "garlic breath". Doesn't keep vampires away, either.
This affects the coffee as well, producing a light, bright, lightly acid coffee.
Most of the coffee goes to the main market at Goroka, and is blended from all the plantations and small holdings. So, if you see "Goroka" coffee, it is not single-origin, it is a blend of many hundreds of small origins. If you see coffee that says something like Bena-bena, that is a true, single-origin coffee.
Sadly, it is hard to get PNG coffee now, as most of it ends up in blends, along with Java, Sumatra and others. Actually, they don't even say Java or Sumatra any more, they just say Indonesia. So who knows what you are getting.
It's what sold me on an Aldi Coffee Pod machine. A friend made a cup of coffee with a PNG Coffee Pod, and I was so impressed, I bought a machine. The only coffee that is close to the PNG coffee pods now is the Peruvian pods.
Now, all I have to do is find a local supplier of single-origin PNG coffee beans to go with my espresso machine.
After Independence in 1975, a lot of coffee growers handed their plantations over to local land owners and moved do Australia. Many of them have set up plantations in the hinterland of Northern NSW (inland of a place called Byron Bay, if you've heard of it...). Sadly the soil here is millions of years old, unlike the young soils of the PNG Highlands and the Australian grown coffee is nothing like the PNG coffee.