Apple claims to have sold more than a million iPhone 3G units in the first three days since launch.

The millionth handset was sold sometime on Sunday, according to Apple, fewer than three days after the iPhone 3G was made available in 21 countries.

By comparison, the first iPhone model did not reach the one million mark until two and a half months after its release.

"iPhone 3G had a stunning opening weekend," said Apple chief executive Steve Jobs. "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."

That great start was not without its problems, however. An early rush of customers overwhelmed the iPhone's in-store registration system in a number of countries, and users were sent home and told to activate their handsets later.

Despite the early hiccups, the iPhone 3G and the new iPhone 2.0 software have generated a strong reaction from customers.

The new iPhone 3G App Store also reached a milestone of more than 10 million application downloads since its release last Thursday.

Apple estimated that it already has 800 applications on the service, including around 200 which are being offered for free. Of the apps that users must pay for, Apple reports that at least 90 per cent are priced at under $10.

"The App Store is a grand slam," proclaimed Jobs. "Developers have created some extraordinary applications."