Medical Transcription is a big market and hospitals pay well for the service.
Start looking into this market.
There is a startup that I met on Monday at the RockHealth meetup called 'Beyond Lucid' which is changing the way ambulances select which hospital to route a patient to, as well as providing electronic forms for the ambulance encounters to be filled in -- contact them and offer to whitelabel your audio transcription service as a bolt on to their offering
beyondlucid.com - founder is Christian Witt and their chief eng is David Saylor (first name dot last name at beyondlucid.com)
There may be legal ramifications for getting into medical transcription which I am not aware of though (bond insurance etc.) -- should be easy enough to figure out though.
Talk to the guys at Dr Chrono. I think this was a feature they were asked for - again, it may be a license/whitelabel opportunity.
edit:
One application which would be amazing would be to have this service coupled with an app like Phone Tap (getphonetap.com) where I can record a phone call, then with a click upload and have it transcribed and emailed to me.
This would be great for consumers fighting phone companies, and customer support/call center applications if you could run it and capture phone audio somehow...