It is being held at Yerba Buena Center for the Arts Theater, where Apple has held many product launches.
The new model is expected to work with fourth-generation, or 4G, cellular networks. That capability is something Samsung’s Galaxy S III and many other iPhone rivals already have. A bigger iPhone screen is also possible. The new model will likely go on sale in a week or two.
Still unknown is whether Apple will announce a smaller version of its iPad on Wednesday.
Apple dominates the market for tablet computers, shipping seven out of every 10 tablets worldwide in the second quarter, according to research firm IHS iSuppli. Rivals have been trying to compete by producing smaller, cheaper models -such as Amazon’s Kindle Fire. A mini iPad would challenge those relative newcomers.
Sales of Apple’s iPhones are still strong, though the company lost the lead in smartphones to Samsung this year. Samsung Electronics Co. benefited from having its Galaxy S III out in the U.S. in June, while Apple was still selling an iPhone model it released last October. A new iPhone will allow Apple to recapture the attention and the revenue.