It might not look like so, but your iPhone does have a file system, the thing is that is not the kind of file system that we are used to. To save your data you will only have a directory and you won’t be able to choose it.
If you have an iPhone you might notice that there is no application that has a save button, all your apps save data transparently a few seconds before you quit it.
This is not magic, you have to apply some techniques that i’m going to show you.