Five years ago today, Apple unveiled the original iPhone to the world. It wasn't a tightly kept secret, shrouded in mystery and speculation like more recent Apple announcements, but it was arguably the world's most anticipated gadget launch.Although its form factor -- a capacitive touchscreen candy bar hasn't dramatically changed over the years, each iteration of the iPhone has yielded important improvements. Let's take a look back at how the iPhone revolutionized what we thought a phone could be.