Google's secret project x was thought to include glass developments.
Whether or not someone is about to introduce a transparent phone, here's an interesting take on why nobody had done it as of May 2014.
We asked OLED designer Jan Hesse of the Fraunhofer Institute in Freiburg, where they've designed transparent OLED lighting panels, and he told us "it's a matter of very poor contrast. Due to the fact that with transparent screens the background is visible…and the brightness is lower than with standard single side emitting OLED displays." It goes on to explain what solutions the various smartphone makers have tried -- nothing that sounds like SPD, but the article is more than 3 years old.