For the third-quarter calendar year period (July - September) Samsung sold 18 million Galaxy S3 handsets, while figures show that Apple only sold six million iPhone 5 models.
The figures are slightly skewed, however, as Apple released the iPhone 5 handset on 21 September, meaning it was only on sale for nine days of that quarter. While the Samsung Galaxy S3 was available for sale for the solid three months.
Another way of looking at this is that Samsung managed to outsell the iPhone 5, but only if you include a period of time when people physically couldn't buy an iPhone 5.
Or another way of looking at it is Samsung sold 18 million phones in 61 days; Apple sold 6 million phones in 9 days. Therefore Samsung sold 295,081 Samsung S3 handsets a day; Apple sold 666,666 iPhone 5 handsets a day.
So for every Samsung S3 bought, Apple sold 2.26 iPhone 5 handsets.
Of course, the sales don't sit steady like that: they start with a peak. According to an Apple press release, Apple sold five million iPhone 5 models in the first three days, and we can presume another million in the six days following (during which iPhone 5 availability was limited due to supply problems).
The same figures show that Apple also sold 16.2 million iPhone 4S handsets during the third calendar quarter.
Apple also announced that it had sold 26.9 million iPhone handsets in total during the fourth fiscal quarter (which runs on different months to the calendar quarter: August - October). Although Apple does not provide details between iPhone 4S and iPhone 5 models.
The iPhone 5 remains in relatively short supply, however, and is currently listed with a 3-4 week dispatch time on the Apple UK store. The delays are, allegedly, due to supply issues at the Sharp factory that creates the iPhone 5 display.