"This is life in the smart phone world. Phones are not perfect. Most every smart phone we tested behaved like this," he said, referring to the controversy as "Antennagate".
Apple will offer the free cases only through September 30, suggesting Apple expects the issue to be fixed by then.
However, Jobs promised that Apple will offer a full refund within a month if iPhone 4 users are still unsatisfied.
Apple has sold more than three million units of the iPhone 4 in the three weeks since its launch, he added.
But some iPhone 4 users have complained that they lose reception when covering the lower left corner of the phone.
Jobs said he first heard about issues with the wraparound antenna - which some experts had hailed as an innovation - 22 days ago.
He called media reports that he had known about the issue before the June launch a "total crock".
Initial response criticised
Analysts and communications experts say the "Antennagate" controversy was less about a flaw in the iPhone than Apple's response to it, which some have criticised as dismissive.
Apple initially advised consumers to hold the phone differently. Then, earlier this month, it blamed the problem on a software glitch that overstates signal strength.
But Richard Munarriz, of the Motley Fool, said Apple's reasoning "seems a bit over-the-top".
"[They are] saying, 'Hey, we're not the only ones with our hands in the cookie jar,' blaming everybody else where Apple is supposed to be this aspirational brand above everybody else," he said.