A while back, we ran a feature on the best vintage camera apps for the iPhone, one of which was a Polaroid app. If you want to complete the look, you need Photoroid by Ryan Astle.
As you might have guessed, it converts your iPhone into a Polaroid camera. At least, in looks anyway. You get artwork for the back of your phone, with a smaller piece for the front, combining to create that vintage-style look.
It fits all iPhones, takes around five minutes to apply (and less to remove), with an online price of $14.99.