This is minor, but I might consider adding a "goodbye" stage that happens at the end of each path through the IVR.
I felt caught off guard a little by the app hanging up on me after the directions ending. And right now the planet selection endings play once, then play again, then hang up - I was expecting them to either play once and hang up, or loop forever.
A final route for each path that makes it clear the IVR is over. Maybe something like:
"Thank you for calling the ET Phone Home Service - the adventurous alien's first choice in intergalactic travel."