32GB has up to 26GB available for user data, I don't know what AT&T installs on it and how much memory it uses.
My 925 (16GB) came with good 12GB of space for user data.
16GB is very little, especially if you intend to take lots of photos (which are already 2~3MB on 925, they must be much bigger on 1520 in full resolution). If you'll only use a couple of apps, it's okay though, but if you intend on installing lots games, you'll quickly run out of memory. I really wish they had the 32GB 925 here, 16GB (12 actually) is very little.