Despite a few hiccups and stores running out of inventory, Apple was able to sell one million 3G iPhones worldwide across 21 countries its first three days on sale. During that same time, owners of both the new and old iPhone were able to download 10 million apps from the newly launched App Store on iTunes, despite major problems with the iPhone 2.0 software update disabling many people’s phones temporarily on Friday.

That brings the total number of iPhones sold since the launch of the first generation phone to more than 7 million. Apple’s goal of reaching 10 million iPhones sold by the end of the year seems well within reach. In contrast, it took the first iPhone 74 days to reach one million sales, but it wasn’t sold in 21 countries. Apple watchers will be looking for clues about what portion of sales are in the U.S., versus in international markets.

The startup community will be more interested in the download numbers. The 10-million download figure includes both paid and free apps. Apple did not offer a breakdown, but it stands to reason that the free apps made up the vast majority of downloads.

But even if 10 percent were paid downloads, though, and assuming an average price of 4.99, that would be a $5 million weekend. Not a bad start. And it could have been more than that. Seven of the top ten paid apps, including Super Monkey Ball, Cro-Mag Rally, Tetris, and Band, are $9.99. (Coming in at No. 12 is another $9.99 game, Electronic Arts’ official Scrabble, which is also coming to Facebook).

Some of the apps seem to have been rushed out too early, with reports of some of them crashing. So the launch wasn’t perfect. But the demand for the new iPhone and all the apps made for it indicated by these early numbers support the notion that people desperately want the Web and better computing experiences on their phones. Of course, we knew that already.