I have an 8gb iPhone 4 but only 6gb in storage?

On the box it says 8GB but when I look on the settings it says 6 GB. My brother and I share the same plan. And my mom told me that we have 6GB to share. So I have 3 and he has 3GB. I'm confused because I'm using more storage than him. Mine says I have 5.4 GB left but my brothers says he has 5.7 GB left? Do we have 8GB on the phone plus the 6GB or do we both have to share 3GB? By the way we use AT&T.

When apple installs ios on it, it takes up tons of space. That's a way they get you. They say 8GB, but with the operating system it really only has around 6.