While working on a ladder, my cell phone slipped away out of my hand.
Bad fall cracked the screen, grrrr.
Current solutions to this bad rounded cell phone designs are cell phone covers, anti-slip stickers, ...
but I don't want that, sometimes it is ugly or you get a thick phone (case).
To avoid a fall would happen again with the new cell phone, I made some dots out of Ikea's Patrull tape
and a hole puncher, and sticked them at the side, just enough to give grip at my palm.
It works great !
Do not stick the dots at the back of your phone, because they could make scratches on smooth surfaces.
Also while punching the dots, and sticking them at the side of your cell phone,
and when you are done, make sure your hands are clean while using your phone,
otherwise you could also make scratches on your cell phone screen.