With an iPhone, can you only get music through iTunes?

Can you download music elsewhere without having to go through iTunes?

Yeah. Simple way, just drag and drop any music file into the itunes library then sync.

If you have do jailbreak, then you can use itools to download the music from computer.
or Install a software like TuneWiki from APP, then you can download music from internet directly.

No, you can add any mp3 song into your itunes list, then copy to your phone, I do it all the time with all my mp3's I already have.

Yeah of course you can get all the music from iTunes. And in the professional site of iTunes all the music, music player, movies, show all are available and there no need of extra site. But if you want to visit another site then as far as I know jailbreak is necessary.

You would have to use iTunes to put the music on the iPhone but no, you don't have to buy the music from iTunes.