When iTunes was launched, it sold one million songs in a week for 99 cents each.
You had the luxery of playing the music stored in your Music Beta by signing in with your Google account. You could listen to music on your iPhone after signing in with an app called G-Music.
An app similar to G-music, called aMusic launched by Amazon also served the same purpose. This app would have enabled you to play music in your Amazon storage locker on iOS. However, unfortunately, this cannot happen.