Some folks have done the math and it looks like Apple sold it's 500 millionth iPhone sometime in the past few weeks, but they've been quiet about it.
It took them more than three and a half years to sell the first 100 million, but have sold another 400 million in about the last 3 years. When Steve Jobs announced the iPhone in January of 2007, he set a goal of reaching 1% of the global handset market in 2008. At the time, that represented about 10 million phones. Here we are at a cumulative total of 500 million iPhones. Pretty impressive.