This Classic Yugoslav design was made in various vibrant colours, apart from grey of course. The outward design was introduced in 1965 as the ATA 30 series. The ATA had traditional innards, ATA meaning Automatic Telephone Apparatus.
The ETA 30 series had a pcb and electronic components, ETA standing for Electronic Telephone Apparatus. The ETA 30 series was introduced in 1976.
There is an ETA 31 and a 32. I was not able to find out what the difference is. It does not seem to be the presence of an earthing button.
It is a rather compact telephone. It has a smaller footprint than a T65 and is a little lower. The handset is shorter too. It is very lightweight, but the handset seems to be unexpectedly heavy. It feels like some weight was added to it.
Also it looks like this model could be converted to a wall phone, by replacing 2 of the rubber feet with a single wall bracket, changing the clear plastic switch hook assembly for a different model, and turning the dial around.
My specimen was given to me by a friend living in the area of the former federal republic of Yugoslavia. I scrutinized it pretty much completely but could not find a production date on it. The only parts dated are the microphone element and the receiver element, dated 82 and 86 respectively.