Ungrip adheres to most flat, non-porous surfaces. It will not stick to rubber, soft-touch silicone, TPU, fabric, and those with waterproof coating.
For slightly curved phones like HTC M (7,8,9) series and LG G (3,4) series, Ungrip will work on them with no problem. You'll just have a bigger gap between the phone and the Bumper on both sides.
Ungrip doesn't adhere well to Sony phones due to their waterproof coating.