Apple is expanding its line of U.S. iPhone retailers this September to a whopping three, by adding giant Best Buy on the list. The iPhone currently has only two official retailers in the U.S., Apple and AT&T, which is also the official U.S. carrier for the device.

The arrangement is sure to be profitable, considering it’s just in time for holiday season. Best Buy will begin selling the new 3G iPhone on September 7, in both options - the 8GB and the 16GB models. The only Best Buy stores that won’t sell the iPhone are those located in areas where the AT&T wireless service is not available.

The deal comes as response to the “enormous demand” Apple has been talking about lately, spreading the iPhone to 970 more U.S. locations, including the Best Buy Mobile shops.

Customers currently have a waiting time before they are able to get their hands on an iPhone, but as the number of iPhone-selling shops grows, the waiting period is expected to shorten as well.

Last month Apple revealed impressive iPhone sales in just three days after the launch of the 3G model on July 11: one million units.

“It took 74 days to sell the first one million original iPhones, so the new iPhone 3G is clearly off to a great start around the world,” Steve Jobs said at the time.

At the same time, Apple has reportedly begun working on the supply problems, by increasing the production of iPhones to 800,000 per week, which could be a sign that they are preparing for the 10 million units sold goal.

The price for the 8GB model is $199 in the United States, while the 16GB model costs $299. In order to become the proud owners of an iPhone, buyers must also agree to sign a two-year contract with the U.S. official carrier, AT&T.

Earlier this week, Steve Jobs also revelead that more than 60 million applications for iPhone were sold in just one month through AppStore.