How to implement conversion of voice to words (speech recognition) in Qt?
Qt itself does not provide speech recognition. You either have to use third party software component, use a web service or implement it by yourself (don't ask here how - it is way too complex topic to discuss it here). One example for a web based speech recognition: http://datamarket.azure.com/dataset/bing/speechrecognition
There's a work in progress module call QtSpeech that you might be interested in.