Excitement over the new iPhone is building to a frenzy this week as rumors abound that Apple (AAPL) will unveil upgraded models on September 10.

That would be almost exactly a year after Apple introduced the iPhone 5, which grabbed the title of best selling smart phone model in the world last year.

Apple isn’t commenting on new models yet but the September 10 introduction date has been confirmed by major news organizations including the Wall Street Journal’s AllThingsD and dedicated Apple bloggers such as Jim Dalrymple.

The rumored new handset, expected to be called the iPhone 5S, will probably look quite similar to the current model 5 but is sure to be lighter and more powerful than ever. It may also be accompanied by a lower-priced, plastic-cased model, dubbed the iPhone “5C” on the Internet.

Pictures leaked onto the Web of the purported lower-priced iPhone show an array of bright colors instead of…