There was an article about production at foxconn (where they make the iPhone 6 and 6+) saying they are cranking out 140,000 6+'s per day and 400,000 6's a day. That's 21.6 million combined units in two months if they work 5 days a week. Obviously more units if they are working 7 days a week. Like, 30.2 million combined units.. by, say, mid-october.
21.6/30.2 M combined units globally, that doesn't go into details as to how many are earmarked for the U.S. or any other country. Whether or not the guy on reddit was right or not is another question all together but Apple I'm sure has projected amounts earmarked for carriers globally.