4Gb Storage: Why can it only use 1.6GB? Why do Android phones say they have 4GB storage but then cazn only use 1.6GB of it? Why is this? Is it possible to access all that other space?

If you see below it confirms how much space this phone has and how little (except for Apps) it really is using. Any advice how I can make the phone use all the available space?

Edit Its a Huawei Ascend
You are only able to use 1.6 gig because 2.4 are required by the android system. This includes all 'the code' and default apps, ringtones/sounds, backgrounds etc. You can free some of this by rooting your phone and using tools but to expand beyond this you will need to add a micros SD card.
I sympathise with you, this is a very annoying niggle all android providers do. can confuse many people. (with a 16gb s5 you get about 10 gig of space)