That means Apple improved its failure rate by 62% in the last two years, Tseng said, while RIM cut its dead-smartphone rate by 47%.

Tseng called the Apple and RIM improvements "pretty impressive."

But while Apple's iPhone 4 leads the reliability pack, it's the smartphone most likely to break during a year, according to SquareTrade's accidental damage claims.

"In accidental damage, it's exactly the reverse. By far, the iPhone 4 breaks the most frequently, although we're also seeing a lot of claims from Motorola and HTC owners," Tseng said.

More than one out of seven iPhone 4 owners, 13.8%, to be exact, will file an accidental damage claim with SquareTrade in a year, the highest rate of any smartphone. Motorola and HTC owners reported damage claims at the same 12.2% rate, but only 6.7% of BlackBerry users filed claims during the same period.