This one is loaded with several ingenious hacks from the 70s/80s era.
The original model was created by [Henry R. Feinberg] of Bell Labs specifically for the movie. It was built with the intent that it would be worthy of conversation between gurus; after toying with microwave ovens and non-portable devices, Feinberg came up with exactly what you see in the film...a disc with a recording, a translator, and a long-range transmitter. According to E.T. lore this was in the form of a saw blade, Speak and Spell, and an umbrella...with a few critical details in between.
This may be one of the Godfathers of hacks. It's not common to see such physical, working, plausible models in movies these days; a device that actually works is horribly rare since the advent of 3D animation (because you can fake it).
We'll see how accurate this build is, and whether or not E.T. could have actually texted his buddies with a homebrew device.