No more storage left in iPhone 3G?

I tried downloading more apps and taking more pictures, but it said I had no storage left.So, I went into Settings > General > Usage and it said that I had 0 bytes Available, and I have 6.2 GB Used, but the only things I have on my phone is Music which is 2.0 GB, and Photos & Camera which is 1.2 GB. As for Videos, there's no data, which is correct. This is all only 3.2 GB, so why does it say that I used all my storage?

Factory apps already stored on the phone like your messages and settings ect ect when they tell you its a 16gb storage or whatever thats basically a lie the phone as a whole has that much storage but not for your personal stuff about 3-4 gb are the phones factory apps and whatever else, back it all up onto a memory stick then delete it all then continue to take pics/videos or download apps ect