Apple Inc. had sold 1.7 million units of the iPhone 4 worldwide by Saturday, June 26, its most successful product launch yet, the company said Monday.

Sales of the touchscreen smartphone, which competes with devices from Nokia, Research In Motion and Motorola, surpassed some analysts’ expectations, as well as those of Apple itself, which has been having trouble keeping up with demand.

In a statement, Chief Executive Steve Jobs apologized to “customers who were turned away” because the company did not have enough supplies of the iPhone 4.

Shares of AT&T Inc, the exclusive U.S. provider for the iPhone, rose as much as 1.5 percent after the news as analysts said it meant more customers than expected committed to use the No. 2 U.S. mobile provider’s service for another two years.

This is seen as more crucial than ever because AT&T is widely predicted to give up its exclusive rights to the phone in the next year, when Apple is expected to add Verizon Wireless, the biggest U.S. mobile operator, as a service provider.

BTIG analyst Walter Piecyk estimated that about 500,000 of the iPhone 4 sales were to AT&T users.

“This could be the last exclusive iPhone AT&T gets so it’s therefore the most important one  … It certainly was a huge success for AT&T,” Piecyk said. He noted that some investors were not celebrating yet as they ultimately expect AT&T to lose a lot of customers when Verizon starts selling iPhones.

The iPhone 4, which boasts video chat and a longer battery life, launched last week with fans lining up outside stores overnight by the hundreds.

Hudson Square Research analyst Daniel Ernst said the 1.7 million number likely included pre-orders, which began on June 15. He said the phone appeared to have sold out in some stores this weekend in New York, Connecticut and Maryland after the official launch on June 24.

Ernst said his rough estimate was for sales well north of 1 million. “This is closer to 2 million so it’s above our expectations,” he said. “No single smartphone model has been this successful.”

Apple started selling the phone online on June 15, when both Apple and AT&T websites faltered amid heavy demand, causing delays to many customer orders.

Verizon Wireless, a venture of Verizon Communications Inc and Vodafone Group Plc, is countering iPhone by heavily promoting phones based on Android software from Google Inc.

Apple’s shares were up $1.05 at $267.75 in early afternoon trading on Nasdaq. AT&T shares were up 25 cents at $25.04 on New York Stock Exchange.