Those of you who are used to using Dragon Naturally Speaking will know that you can use a digital voice recorder for deferred transcription. Once your Dragon is trained you can record audio onto a digital voice recorder and then play the audio from the recorder into Dragon for unattended transcription.
Using the Transcription Pak with iListen deferred transcription is possible. MacSpeech have certified the Olympus DS-2300 for use with the Transcription Pak on iListen.
http://www.macspeech.com/article_info.php?articles_id=270
