A new survey finds the iPhone to be one of the most reliable smartphones on the market—provided you don't let it slip through your fingers. Turns out glass touchscreens and gravity don't mix.

TechCrunch got its hands on this report (warning: PDF) from SquareTrade (an online retailer of extended warrantees) about failure rates for leading smartphones, including Palm Treos, BlackBerrys, and the iPhone.

[Note: SquareTrade says it culled 22 months of statistics from about 10,000 iPhone owners, all of whom had signed up for extended iPhone warrantees from the company—and as TechCrunch notes, SquareTrade is in the business of selling smartphone warrantees, so keep that in mind as we rifle through the report.]

The results? Quite interesting. First of all, when we look at the iPhone's overall failure rate, it turns out that more than 30 percent of iPhone owners in the survey experienced some type of hardware failure over a two-year period.

Wow—sounds like a lot, right? A closer look at the numbers, however, reveals that just under 10 percent of the iPhones surveyed failed due to "normal" use (i.e., they just up and died one day).

Indeed, according to SquareTrade's figures, more than 15 percent of BlackBerry phones fail after two years, or nearly 20 percent when it comes to the Palm Treo. (The SquareTrade report doesn't specify particular BlackBerry or Treo models.)

So, if only 10 percent of iPhones are croaking after "normal" use, what's with the other 20-odd percent? You guessed it: Close encounters with the ground.

Taking accidental failures as a whole, SquareTrade found that 66 percent of said accidents involved dropped, fumbled, tossed, or otherwise airborne iPhones that land smack on a hard surface, cracking the 3.5-inch glass touchscreen and rendering the handset pretty much useless.

The next biggest enemy of the iPhone? Water (or "water immersion," to be more precise), with 25 percent of surveyed iPhones falling victim to good-ole H2O. Common scenarios: swimming pools, "fishing trips gone awry," and drops into drinks, sinks, and toilets (ick), according to SquareTrade.

A final 8 percent of iPhones met their demise in the form of car tires, lawnmower blades, fire, and the restless jaws of household pets.

The moral of the story? The next time you pull the iPhone (especially the 3G and 3GS models, with their glossy, slippery shells) out of your purse or pocket, do so carefully. And if you've got butterfingers (like my wife, who drops her iPhone every five minutes or so), consider a rubberized case for your iPhone to protect it from falls.

So, quick show of hands: How many of you have cracked your iPhone's glass screen after dropping it? How about dips in the water?

Related:
iCrack: The iPhone Is An Accident Magnet [TechCrunch]