As you can see in the video below, all they have so far is a very very early prototype, almost just a proof-of-concept, but the team expects to have a more fully functioning prototype with working software by the end of the year. You'll also notice that the device isn't 100% transparent, because some components - the battery, SD card, and microphones - simply can't be made transparent right now. Still, it's a pretty cool start.
The display is what Polytron calls Switchable Glass technology, which is a conductive OLED. When the phone is powered off, the liquid crystal molecules in the display are a cloudy white, but when you turn on the juice (electricity running through transparent wires), the liquid crystal molecules realign to form text, icons, etc.
There is no word on when the displays will go into production, but Polytron general manager Sam Yu says it will be "near the end of 2013". Yu also said that Polytron is in serious discussions with "major smartphone makers" across the US, Europe, Japan, and South Korea to bring the display to market.