You need to think about more than impact trauma to protect your phone. Moisture and dust can be just as much trouble.
Most protective phone covers are primarily designed to limit the damage from impact trauma, such as these four heavy duty covers to stop your phone getting smashed or scratched.
It's a good list, but heavy objects and pointy things aren't the only threats to your smartphone once you step away from your desk.
Dust and moisture are far more subtle, but can still take their toll on your phone - whether you're combating sand, mud, plaster dust and coffee spills or rain, hail and snow.
You'll find water and dirt-proof gadget cases from various brands including LifeProof and InDepthCases, as well as waterproof options from the usual suspects such as Otterbox and Griffin.
LifeProof is a new entrant into the Australian market. They have the LifeProof Case for the iPhone 4/4S and LifeProof Frē Case for iPhone 5. The press release states that are "completely waterproof down to 2 metres" and designed to "survive a drop of 2 metres". They cost $79.95.
If you find these cases a little cumbersome and you don't need that kind of protection all the time, you might also consider a water and dirt-proof pouch from the likes of Simplism, Beachbouy, and Amphibx.
Cases are generally custom-designed for one device, whereas pouches tend to have enough room to support a range of Apple, Android or Windows devices.