Why the iphone first generation had a black botton?

Https://www.google.com/search?q=first+iphone&hl=en&client=safari&source=lnms&tbm=isch&sa=X&ei=ouFdUcOKOuTXigLa9oHgDg&ved=0CAgQ_AUoAQ&biw=320&bih=416#biv=i%7C3%3Bd%7CJw0wEPZ1CXHpGM%3A

That's where he antenna is the made it black so people can know where it is and people can easily repair if if need be

That was the antenna. It wasn't until later models that Apple realized it's an eyesore, so they made the antenna smaller (as you can see on the new iPhones around the medal band) and more discreet.

That was where the antenna were stored for the phone. It also had an aluminum top 3/4. Wi-Fi signals don't pass very well through that hence why the bottom was different.

It's black plastic for the antenna because cell and wi-fi signals do not pass through metal.