I took a course at my gliding club leading to a CAA radio operator's license (FRTOL) a couple of years ago. It takes you through the main messages you need to know for proper use of a VHF radio in an aircraft.
The app now displays a phonetic version of the message as well as speaking it out loud. It might be used for learning, or if you speak to Air Traffic Control occasionally, and want to be confident you're close to CAP 413 wording.
I was able to use App Inventor blocks to tweak the audio output to conform to required standards - e.g. "three" is pronounced "tree". There's a place to enter emergency numbers, and a panic button that will send your GPS location and a Google maps location to an email address or as an SMS.