Due to Apple policy, it's impossible to download music on iPhone with common browsers like Safari, Chrome, Opera, etc. So, you need the help of Documents, its built-in browser allows you to download songs and videos from the web. Install Documents and launch the app. Tap the blue compass icon at the bottom right to open the built-in browser in Documents. Tap the blue compass icon at the bottom right to open the built-in browser in Documents. Navigate to Free MP3 Finder, which is a free music download site. Find a song, tap the download button, and select an MP3 bitrate to start the music download process. After the song is saved, you can check it in the download manager at the bottom of the screen.