What is the difference between iphone covers and smartphone covers?

What is the difference between iphone covers and smartphone covers?

Phones come in different shapes and sizes and have buttons in different places. If you buy the wrong cover, it won't fit.

Just like the different versions of iPhones, iPhone 3 cover will not fit on and iPhone 5s or iPhone 6, different smartphone models will be different shapes and sizes, with different button, screen and accessory cut outs. So that is why the cases are different sized. The more fragile a device is, the bulkier the case will tend to be in most cases.