"A lot of people told us (a) bumper solves the signal strength problem," Jobs said Friday. "Let's give everybody a free case. Every iPhone (4) user is going to get a free case" through Sept. 30.
Users who bought a case can get a refund, Jobs said at the company's Cupertino, Calif., campus.
Getting a cover, however, may not be easy, he warned.
"We can't make enough bumpers," he said. "No way we can make enough."
To counter that issue, Jobs said other covers would be fashioned to handle the iPhone 4's antenna issue, can be ordered online and "zoom, we'll send it off to you."
The fix would cost about $45 million, CNBC analysts said.
Wall Street reacted positively to the news, with investors pushing Apple shares up within minutes of the announcement of the corrective measures.
To achieve a sleeker, lighter phone, designers snaked the antenna around the device. Within days of consumers waiting hours in line for the coveted device, reports began surfacing on the Web that the iPhone 4 could lose a signal, or that the signal indicator would show a weakened signal, when the device was gripped in a certain way, particularly if held in the left hand.
Consumer Reports withheld recommending the fourth generation of iPhone, saying its engineers tested three iPhone 4s and found that when the bottom left corner of the iPhone is touched it could lose signal strength or drop a call.
Jobs also said an algorithm that showed an incorrect number of signal strength bars had been corrected and was available for downloading, CNBC said.
A live feed of Jobs' remarks wasn't permitted but CNBC provided updates from producers in the audience who sent updates via Twitter. Clips of the news conference also were provided on a time-delay basis.
Jobs called the smart phone "perhaps the best product we ever made at Apple," saying more than 3 million devices were sold since it was released June 24.
Jobs opened the news conference with a mea culpa.
"We're not perfect. We know that. You know that. IPhones aren't perfect, either," he said. "But we want to make all of our users happy. ... That's what drives us to making these products in the first place."