Chinese smartphone start-up Zuk demonstrated a concept/prototype smartphone that uses a large transparent OLED panel. All we currently have is the video below:
It's not clear whether this is even a working transparent OLEDs. While we have seen larger transparent OLEDs (for example Samsung's soon-to-be commercialized 55" transparent OLED panels) it's not clear when smartphone-sized transparent AMOLEDs will be released commercially for such applications.
Currently the only transparent OLEDs on the market are small (around 2") PMOLED displays. In 2011 Lenovo released a feature phone (the S-800) that used a small transparent PMOLED, and in 2012 Indonesian Nexian released a similar phone called the Glaze M-9090.