The forecast comes by way of Piper Jaffray analyst Gene Munster, who notes the half-million mark would compare to sales of 1 million iPhone 3G handsets during its inaugural weekend last July, and 270,000 original iPhones back in June of 2007.
"Several factors lead us to believe Apple will sell less iPhone 3G S's at launch than it did for the iPhone 3G including a less Â dramatic change in value proposition and fewer available countries at Â launch," Munster wrote in a research note Thursday.
More specifically, the analyst points out that the launch of the iPhone 3G last year came alongside a 50% price reduction from the original models, which drove sharp increases in demand.
With most customers being able to purchase the new iPhone 3G S at identical pricing, the change in value proposition for the new model is therefore not as meaningful as last year, he said, which should likely translate to fewer units sold at launch.
In supporting his lower unit sales estimates for launch weekend, Munster also noted that the iPhone 3G S is launching in just 8 countries this weekend compared to the 21 countries that were able to launch the iPhone 3G on its first weekend last year.
"The iPhone 3G S launch and the price reduction on the iPhone 3G leave us increasingly confident in our 5 million iPhone unit estimate for the June quarter," the analyst told clients. "Our estimate includes 3.0 million iPhones in the month of June, approximately 500k 3G S units in the back half of the month and the remaining 2.5m iPhone 3G units through the entire month."
For the September quarter, Munster expects Apple to sell roughly 7 million iPhones combined. He maintained his Buy rating and $180 price target on shares of the Cupertino-based company.