Jobs also promised that iPhones would be available in June. Apple delayed the release of its new Leopard operating system for Macintosh computers so engineers could devote their efforts to the iPhone.
A supposed internal Apple memo leaked last month indicated concerns that iPhones might not make it to market on time.
"There have been a lot of rumors of significant problems with the product," said analyst Rob Enderle of Enderle Group in Silicon Valley.
"What Apple is trying to do is put those rumors to rest and take pressure off stock prices."
The device, to sell at prices of 499 to 599 dollars, will be distributed in the US market through ATT, the new name for the Cingular Wireless brand.
It will weigh 135 grams (3.8 ounces) and have the Apple OS X operating system and four or eight megabytes of storage. It will be able to play videos as well as music and have a screen of 3.5 inches (nine centimeters).
Analysts are divided on whether the iPhone will be an industry-changing device or be too expensive to compete with other smart phones such as the BlackBerry.
On its website, Apple said the iPhone will include "a revolutionary mobile phone, a widescreen iPod with touch controls, and a breakthrough Internet communications device." It will also include a two-megapixel digital camera.
A second-generation iPhone is "already being rushed out," Enderle said.
Taiwan-based manufacturer Quanta Computer is reported to have a contract to build millions of next-generation iPhones that are to begin shipping before the end of the year.
"The iPhone has a number of shortcomings and now that it is in the final phase of testing Apple can pinpoint what those are and fix them in the second-generation," Enderle said.
"As a gen-one product, no one in the industry thought Apple was going to hit one out of the park. Especially with this being their first phone."
Among the flaws in iPhones are built-in batteries likely to run out of useful life in approximately a year based on common recharging patterns, according to Enderle.
ATT has already received more than a million inquiries about iPhones.
Working with ATT lets Apple tailor iPhones to the GSM mobile network that is common outside the United States. The iPhone is to debut in Europe by the end of this year and in Asia in 2008.
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