Improved version - http://www.thingiverse.com/thing:807105
This is based on http://www.thingiverse.com/thing:724526
I started using droidplanner with my APM 2.5 based quadcopter and needed a way to attach my phone to my transmitter.
The mount is designed around my LG G2 in an Incipio case. Modify the clips for other applications.
The clips hold an OTG cable which in turn holds a 3DR radio. http://www.thingiverse.com/thing:41536
The pieces were printed in PLA at .2 mm layer height and 100% density. The center mount piece is tapped with M3 threads. Printed pieces hold threads surprisingly well. M3x12 socket head screws hold the clips to the center piece.
An M4x45 flat head screw holds the mount to the transmitter bracket. A nut secures the bolt to one side of the arm. The well in the thumb screw holds an M4 nut.
JR9303_phone_bracket_2a.stl has a simple bracket with a shorter thumb screw. A single clip feels too flimsy for me but it may be fine for lighter devices.