Any API for this or any Help, plz tell me. (I am thinking about this is through interaction to the server where will be the voice recognition parser or API etc..)
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You may wish to refer to the answers in the following questions:
In short, there is no API for this on the iPhone, although there is a private Voice Services framework on the iPhone 3GS for going the other way, from text to speech. Given the computational limitations of a portable device, your best bet would be to implement this voice recognition on a backend server, like Google does.