I struggled with the instructions, push with thumb just was not cutting it. This might be a little tough to pop the first few times.
What I had to do was this;
- Place phone in face down in the palm of your left hand with the USB jack pointing towards you.
- Place your right palm on the back side of the phone just above the USB jack.
- Press your hands together and try to push the back away from the USB jack.
The first time it popped off with almost a click feel. Seems like it will get easier over time as well, once you know how to actually get the damn thing off.