Apple is to offer iPhone customers who bought the device before a sharp price cut a $100 store credit, chief executive Steve Jobs said.
The Apple iPhone
The offer applies to people who bought iPhones at either Apple or AT&T stores and who did not get rebates or other considerations, Jobs said on Apple's Website.
While Apple has not disclosed how many units it has sold to date, it has reported selling 270,000 iPhones on the first two days and expects to sell one million units by the end of September, potentially costing the company tens of millions of dollars.
Apple shares fell 1.2 per cent to $135.06 in late afternoon trading on Nasdaq.
"Even though we are making the right decision to lower the price of iPhone, and even though the technology road is bumpy, we need to do a better job taking care of our early iPhone customers as we aggressively go after new ones with a lower price," Mr Jobs said.
Apple also has a policy to refund the difference to customers who bought a product within 14 days of a price drop.
On Wednesday, Apple slashed the price of its $600 iPhone model to $400, saying it wanted to make the device - a combination cell phone, music player and Web browser - more affordable. AT&T is the exclusive service provider for the device.