Forbes [ref] recently noted that based on Apple's Q1 2014 iPhone sales numbers (of around 51-52 million iPhones) and on analysts estimates of around 38 million iPhones sold in Q2 2014, the cumulative sales of iPhones (all iPhones sold since 2007) should have crossed 500 million units! This is indeed a significant achievement by Apple, considering the negative sentiments that surrounded the iPhone when it was launched and the extent to which it was ridiculed. It just goes to show that sometimes collective knowledge is wrong and it takes guts to stand up against the majority. But if your product is strong enough, you will eventually succeed, no matter what the so called 'critics' and naysayers called your product (ya am talking about Ballmer here). This number might be slightly off or might not have touched the 500 million mark yet, but it should be in the vicinity.
It is interesting to compare other iDevices' sales from Apple. Here is my plot on this. The plot shows the cumulative sales (in millions of units) sold by Apple since the respective product was launched. Note that 2014 has had only two quarter completed and hence the slight flattening of the iPhone curve. Also notice how the iPod curve changed slope around 2007-08-09, whereas the the iPhone curve is almost exponential, showing no signs of saturation yet. The iPad curve does not seem to have an exponential slope at all, it seems more linear. Either way the iPhone clearly is a runaway hit for Apple, whether or not Apple can match it with any other product in the future (in terms of sheer volume) remains to be seen!