If you have lots of songs you want to take with you everywhere you go but there’s not enough storage on your mobile device, here are some ways to “take” more with you.

Solution #1

Pandora is an Internet, online service that allows you to enter in a favorite band, artist or song and it’ll play you songs that are like them. The basic service is free. Pandora is available on both iOS and Android. Pandora (iOS)
Pandora (Android)

Solution #2

When you want to listen to your specific favorite artists or songs or albums, there are two On-Demand services - Spotify and Rdio. These two services are similar. The service allows you to play from your own library as well as theirs (without buying the song) when you’re online or offline. The free service allows limited listening. Both are available for iOS as well as Android. Spotify (iOS)
Spotify (Android)
Rdio (iOS)
Rdio (Android)

Solution #3

Google Music is a cloud-based, interactive service to store your music, share with others, browse and buy music. You can stream music to your mobile device or sync playlists for offline listening. Google Music is available only on Android. Google Music (Android)