Best free music download app for IPhone 4?

I need a good music download app that:
-I won't need Wi-Fi to use
-I can download as much music as I want
I'll give as many points as I can but I need the app As soon as possible! I'm going on holiday in few days so it's really important because I have to spend 26hours in a car ;-;

This app works for all apple products basically I use it on my iPad, and phone all the time! Its called " Mymedia " it will be in the appstore, then once you downloaded you need to put in a website, the website you need to put in is " www.mp3skull.com " after that you put in whatever songs you want and download! You will have yo go on the website everytime you want to download music and you need Wi-Fi for that, but ONCE the song is downloaded you no longer need the Wi-Fi! Love the app use it everyday for my music!