Some have hailed Siri, Apple's new voice-controlled personal assistant, as a "life changer," but, sadly, the existence-altering feature is only available on the new iPhone 4S. At 9 to 5 Mac, developer Steven Troughton-Smith was able to hack an old iPhone 4 and get Siri to work on it, showing that older iPhones are indeed capable of running Siri. Why then is Apple limiting Siri to the new iPhone? Here, three reasons:

1. Apple wants it to be exclusive
"The first, and most obvious" reason to limit Siri to the iPhone 4S "is that Apple wants to save its 'killer feature' for its latest hardware, giving consumers more of an incentive to upgrade to a device instead of sticking with what they have," says David Murphy at PC Mag.

2. And, to be honest, it's the only exciting thing about the iPhone 4S
"If it hadn't been for Siri, would the iPhone 4S be yet another upgrade and something that most users would pass on?" asks Joel Evans at ZD Net. The new iPhone is faster and has a better camera, but it's not as thrilling as previous new iPhones. "One really cool thing about the 4S, though, is its implementation of Siri."

3. It won't run perfectly
It's also quite possible that Siri won't work as well on the iPhone 4 as it does on the 4S, says Murphy. "Even the slightest hint of performance differences between the iPhone 4 Siri and the iPhone 4S Siri could be enough to eliminate the iPhone 4 from consideration," especially given how fastidious Apple is.