Is there any way, by which we can convert speech to Text using iPhone SDK?
Yes, if you are Google, Dragon, or Siri. The iPhone SDK does not provide any access to the iPhone 3GS's built-in voice recognition, which is apparently none too elaborate anyway. Your best bet is to find a web service to which you can upload audio clips for analysis.
Krishnan ,This is Reply for your Comment Is that the same case for Text to speech?.
No there is Library called OpenEars by using this Library you may achieve the text to Speech functionality.
OpenEars
OpenEars is an open-source iOS library` for implementing round-trip English language speech recognition and text-to-speech on the iPhone and iPad.
http://cmusphinx.sourceforge.net/2010/05/vocalkit-shim-for-speech-recognition-on-iphone/
This looks promising.
As of iOS 10 (not released yet), Apple has their own speech recognition API.
https://developer.apple.com/reference/speech/sfspeechrecognizer
来源：https://stackoverflow.com/questions/2270655/how-speech-to-text-conversion-in-iphone