Amazon Music Unlimited is an “on demand” music service. This is different than Sirius XM which has music channels and pandora which guesses what songs you want to hear. Spotify is the closest competitor where you can ask for specific songs and they are played. In none of these services do you “own” anything, other than the right to listen to music via streaming during the period of your subscription. The cost of data is your responsibility
The service is $9.95 a month or $7.95 for Amazon Prime customers. If you own the Siri-like Echo )$179.99) device, it is $3.95 a month.
“Echo, play me a melody, mr piano man!”
So what is the purpose of radio again?