I recently bought a super cheap Android based touchscreen smart phone. Since I wanted to use on our camera tripod to keep it stationary, I needed a way to attach it. This is what I came up with.
It has worked EXTREMELY well for me as a tripod adapter and as a way to just keep the phone upright.
The adpater is small, lightweight, holds the phone snugly but is easy to put on and take off, and can hold the phone in the exact center without interfering with the volume buttons.
You'll need a printer, a " 1/4-20" nut from the hardware store (probably about $0.23 or so), and a hot glue gun.
1) Print the part
2) Add a little hot glue around the outside of the nut and insert into cavity
3) Add a very thin bead of hot glue to the channel along the inside of the holder
4) Insert phone!