Just a quick example:

final int VOICE_RECOGNITION_REQUEST_CODE = 1234;

void setup() {
}

void draw() {
}

void mousePressed() {
  android.content.Intent intent = new android.content.Intent(android.speech.RecognizerIntent.ACTION_RECOGNIZE_SPEECH);

  // Specify the calling package to identify your application
  intent.putExtra(android.speech.RecognizerIntent.EXTRA_CALLING_PACKAGE, getClass().getPackage().getName());

  // Display an hint to the user about what he should say.
  intent.putExtra(android.speech.RecognizerIntent.EXTRA_PROMPT, "Speech recognition demo");

  // Given an hint to the recognizer about what the user is going to say
  intent.putExtra(android.speech.RecognizerIntent.EXTRA_LANGUAGE_MODEL, 
    android.speech.RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);

  // Specify how many results you want to receive. The results will be sorted
  // where the first result is the one with higher confidence.
  intent.putExtra(android.speech.RecognizerIntent.EXTRA_MAX_RESULTS, 5);

  startActivityForResult(intent, VOICE_RECOGNITION_REQUEST_CODE);
}

/**
 * Handle the results from the recognition activity.
 */
@Override
protected void onActivityResult(int requestCode, int resultCode, android.content.Intent data) {
  if (requestCode == VOICE_RECOGNITION_REQUEST_CODE && resultCode == RESULT_OK) {
    // The list of possible matches
    ArrayList matches = data.getStringArrayListExtra(android.speech.RecognizerIntent.EXTRA_RESULTS);
    if (matches.size() > 0) {
      println((String)(matches.get(0)));
    }
  }
}