-I dont have a SIM Card to pit in it so i cant access the the settings to find out. Or at least i dint know how to get to the settings as it wont let me past the initial set up without a sim.
How to find out how many GB ON iPhone 4s?
Settings > General > About
Scroll down until you get "Capacity." It'll say EXACTLY how much GB you are allowed to use. I have an iPhone 4, and it's advertised to have 16 GB, but when I go to capacity it shows 13.7 GB.
Hope it helps!
EDIT: I just read your actual post. Can you connect it to iTunes and see how much it can store from there?