Apple’s price slashing of the iPhone last week sent sales of the smartphone over the 1 million-unit mark on Sunday, allowing Apple to claim a highly successful launch for its first wireless product. CEO Steve Jobs pointed out it took the iPod two years to achieve the same milestone, and Apple is now primed to consolidate its gains over the holiday season.

But the milestone may be overshadowed by what many consider a huge misstep by Apple, which cut the price of the 8 GB iPhone from $600 to $400 after it had been on the market for only two months. While many consumers rushed out to take advantage of the cheaper device, there were many more that bristled at the premium they paid for being the first adopters. While Apple and other consumer-electronics makers typically drop hardware prices after their initial launch, the high-dollar amount and the timing of the discount so soon after launch took customers by surprise.

In an open letter to Apple customers posted on the company’s Web site, CEO Steve Jobs apologized to early iPhone buyers and offered a $100 Apple Store credit to any customer who bought the device at its original price. But he also defended Apple’s decision to cut the phone price so quickly and so much.

“Being in technology for 30+ years I can attest to the fact that the technology road is bumpy,” Jobs said in the letter. “There is always change and improvement, and there is always someone who bought a product before a particular cutoff date and misses the new price or the new operating system or the new whatever. This is life in the technology lane. If you always wait for the next price cut or to buy the new improved model, you'll never buy any technology product because there is always something better and less expensive on the horizon.”

But he added: “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. Our early customers trusted us, and we must live up to that trust with our actions in moments like these.”

iSuppli estimates that Apple is already the leader in the smartphone market in the U.S. and projects that the company will sell 3.5 million iPhones by the end of the year. Those numbers may be even higher, though, considering the new lower price and boosted sales during the Christmas holiday.