I sometimes want to listen to an audio book on my phone but don't have headphones with me.
So, I wrote
Earpiece, now available for testing, a free app that routes sound through the phone earpiece, so you can listen to audio books (or whatever else) as if you were talking on the phone.
Earpiece also does volume boosting (with or without earpiece-audio functionality) if you want.
You can launch Earpiece as a normal app, or you can launch it by long-tap on the search button.