These models are for the Makerbot Replicator 2X using ABS and dual extrusions. If you use this machine and ABS filament then you will get a very good fit.
I have tweaked the size of the model to work perfectly with ABS and the makerbot replicator 2x. You can modify the .stl files to use with other printers.
When adding the files to the makerbot desktop program, open both .stl files of the desired model before moving one onto the build platform. This will ensure that the two models are in the correct position. Only when you have both parts of the iphone case open on in the view port, can you select both and then move them to the build platform.
I have included the .x3g file incase you get stuck with the .stl files.