Each day Apple is trying to improve the performance of Siri to fulfill the requested features as well as more languages support. With latest study, 87% of iPhone 4S users use Siri each month meanwhile the rest don’t like Siri.
In short, Siri is a smart voice assistant which is very much different from the previous voice command. Apple has made Siri exclusively only on iPhone 4S leaving older device so jealousy. However with help from iPhone hackers, porting Siri to iPhone 4 is possible but it requires proxy server to use Siri.
As stated, Apple has been trying to enhance Siri and of course with the release of iOS 5.1, Siri now supports more languages including Japanese.