This easy beats their record previously held by iPhone 5 at 2 million.
http://www.macrumors.com/2014/09/15/preorders-iphone-6/
http://www.macrumors.com/2014/09/15/preorders-iphone-6/
Apple today announced that it has processed more than four million iPhone 6 and iPhone 6 Plus pre-orders in the first day of pre-launch sales in the select countries that started accepting orders on September 12. This figure doubles Apple's previously announced record of two million pre-order sales for the iPhone 5 in 2012.