According to the latest smartphone Drop Incidence data released by SquareTrade - the largest independent warranty provider in the world, of all smartphones included in the study, iPhone 4 appears to be the one that's most prone to drop damage.
Based on this graph, iPhone 4 is the most fragile device. SquareTrade expects an 11.1% drop-related damage happening on the phone over a year.
SquareTrade went on to suggest that drop damage incidence is directly proportional to the amount of glass found on a smartphone,
The data seems to suggest that the likelihood of drop damage is directly proportional to the amount of glass on the device. With dual-sided glass, the iPhone 4 has twice the fragile surface area of the other smart phones.
So when you have a device as fragile, it's either you --
1. Treat it like a baby or
2. Get one of 'em cases or bumpers.