I use Google Play. My entire iTunes library is on it and anytime I make changes to my library on my Mac it reflects to Google Play.
There's a few Google Play apps, including the official one where you can stream directly to your iPhone.
No fees (Google lets you store up to about 40,000 songs free) and my 10GB library is not on my phone, but still completely accessible.
Oh, and I don't have to use the iTunes app on my iphone (bleh). The third party and official apps all have lockscreen integration (controls and album art).