Tao got an iPhone from his uncle ages ago. It ended the old and good days of using his b&w NOKIA. Tao had thought to get a cover, but the price made him hesitant.
As an alternative, we bought some pads normally being used to pad furniture feet. The idea was super simple: if they can protect pavement from table legs, and wall from handle punch, they should be able to protect the back of iPhone.
We put two on the back, using the height of them to lift the cellphone a bit higher. In this way, camera is always away from tabletop.
In addition, the roughness of pad adds a good amount of friction to the phone. It should work nicely for most people unless you have a putting-everything-to-push-things-down cat, as we do. In general, Tao felt happy about his pads. They are effective, cheap (2 pads cost only 1/20 of a normal cover), and sometimes could be funny!