My 32GB iPhone 4 is my primary "music player" - although most of my "music" is actually audio books and BBC radio programmes. The 32GB model was the largest available at the time I bought it. I may buy an iPhone 5 (rumoured release date is October) and if there's a larger capacity model available then, I'd certainly get that.
My iPhone is basically a music player and a mobile internet device. I probably make about 1 phone call a month on it

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