Current Options
Through The API
You can create a timeline item and add a reply menu item to that timeline. You should be able to have your app fetch that timeline item after receiving a notification with the timeline ID. From that timeline ID you can fetch the attachments including the audio file and the transcription.
Here is an example of the body for the new timeline item:
{
"text": "Hello world",
"menuItems": [
{ "action": "REPLY" }]
}
To see an example response take a look at the Timeline Reference page.
A More Creative Approach
What you could do is create Twilio account to create a number that you can txt message to. You could then have your application interact with the body of the text message.