Blocking outsiders from making programs that would run easily on the iPhone has been one of a series of restrictions that have annoyed users, even leading to some lawsuits.
Jobs, in comments on Apple's Web site, said a kit for developers still will not be available until February, as the company works out how to open up the phone without exposing it to malicious programs.
"We think a few months of patience now will be rewarded by many years of great third party applications running on safe and reliable iPhones," Jobs said on the Web site at http://www.apple.com/hotnews/.
Developers have tried to open up the iPhone for use in the United States on networks beyond Apple's U.S. partner, AT&T Inc, though Apple has blocked many such moves. Spokeswoman Natalie Kerris said Apple has not changed its policy on locking the phone to other networks.
But until now, Apple also had stopped software engineers from creating whatever they wanted to run on the iPhone, without delivering them through the iPhone's Web browser.
Some 200 applications have been created for use on those terms, but consumers and software makers have seen that as an extra layer of rules and technology that was unnecessary and throttled innovation.
Under the new policy, applications will be allowed to run in so-called native mode.
Jobs said he expects malicious developers to focus on the iPhone. "Since the iPhone is the most advanced phone ever, it will be a highly visible target," he said.
Apple could require a digital signature for programs to authenticate their developer, he added, referring to a system that he said mobile phone maker Nokia is implementing.
While this makes such a phone less than "totally open, we believe it is a step in the right direction," Jobs said.
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