23. The method of claim 22 , wherein the modifying comprises modifying the first speech recognition model and the first action classification model by using at least a first N-best list of word sequences corresponding to at least a portion of the audio data, wherein the first N-best list is obtained by using the first speech recognition model.
22. A method comprising: obtaining, using at least one processor, audio data for a plurality of calls handled by a natural language call routing system, automatically obtaining, using the at least one processor, call classification data from the audio data by using a first speech recognition model and a first action classification model; and modifying, by using the at least one processor, the first speech recognition model and the first action classification model based at least in part on the audio data and the call classification data to obtain a second speech recognition model and a second action classification model; and modifying the second speech recognition model and the second action classification model based at least in part on the first data to obtain a third speech recognition model and a third action classification model, wherein the modifying comprises modifying the second speech recognition model and the second action classification model by using the first N-best list or a second N-best list of word sequences corresponding to at least the portion of the audio data obtained by using the second speech recognition model.