Nokia released the 3D models for the back covers of the Lumia 520 and 820 last year as part of their 3D Development Kit. That means it is now possible to a phone to print itself a new back cover, bringing a whole new meaning to DIY accessories.
As far as we are aware RepRap Phone Host is the first mobile app that we're aware of that allows you to 3D print a model directly from a 3D model file (.stl). This has been achieved by implementing a 3D printing slicer that processes the model into a toolpath (i.e. slices a model into layers than are then converted into instruction for a 3D printer). Other mobile apps that support 3D printing are only able to do so through a .gcode file (something that has to be pre-processed on a PC).
RepRap Phone Host is an impressive technical achievement, both on the software side (3D printing slicer) and on the hardware side (the development team has also created a "GAPS" system to ease integration between the phone and RepRap printer.
The electronics design and software development has been carried out by Gerhard de Clercq, while Pieter Scholtz is responsible for the physical manufacturing, mechanical design, and assisting with the user interface design. Making things even more impressive is the fact that both are students attending Die Hoërskool Menlopark (Menlopark high school in Pretoria, South Africa).
Here's a video showing a prototype of the app and RepRap printer in action:
Windows Phone Store description
RepRap Phone Host is a Windows Phone 8 application that allows you to process and then ultimately 3D print STL format 3D models on your "RepRap" type 3D printer running "Repetier" firmware and in possession of a Bluetooth serial bridge.
It includes a STL and GCode render as well as our in-house developed "Bananna Chopper" slicing engine. As far as we know this is the first app the allows a model to be sliced on a smartphone.
To get the app up and running all you need is to add a Bluetooth serial bridge to your 3D printer (there is a tutorial on the RepRap site), pair with it in the Bluetooth menu and then just select it from the drop down menu inside the app and connect to it.
RepRap Phone Host is available from the Windows Phone Store. The app is currently free to download, but is set to become a paid app early next week.
More information is available on the Bananna3D website.