Any 9900 OS will install on it, once you get it. I wouldn't be in a rush to mess with that though. See what it comes with, and take some time to learn the phone first. You're putting the apple way ahead of the cart.
Also, don't jump to conclusions based on OS threads. Everyone's experience with an OS will differ. Even your neighbor on the same phone/carrier will probably argue which OS is best.
How do you know what your getting if you do not have any idea what you have?!? Some work better for others than not. But it is not the case for everyone. Learn the device, break it in, then see where it stands.