Replacing 4 month old iPhone 3GS?

I got My iPhone 3GS in September last year. Recently, the silent switch has begun to play up, and my screen has three dead pixels. This is really annoying, because I saved up the AU $719 myself. I have heard of apple giving people replacement phones before the 1 year warranty was finished. It's only been four months, so can I get it replaced? I am not on a plan or anything, I use prepaid. If so, what do I do? And does this policy work in Australia?