A lot of devices use oleophobic coating on the glass. It is not recommended to use any alcohol-based solutions when cleaning a capacitive touchscreen, neither is it a good idea to apply common household detergents, even if it's stated that they can be used for computer and / or TV screens. The aggressive compounds in such cleaners can easily wipe off the oleophobic coat and leave your glass “naked”.
Cleaning your mobile device's glass should generally be done with just a soft, cotton rag. In extreme cases, water-based solvents should do the trick – cleaners that are specifically designed for touchscreens can be bought at various outlets, just make sure to check the ingredients, as many manufacturers will feel no remorse in stamping an alcohol-based detergent as mobile-friendly. Also, applying the detergent to the rag, rather than spraying it directly on the screen, is a good idea.