It isn't rare for Samsung to sell around 20M-40M worldwide with a Galaxy S phone. The S4 was highly popular like the S II and SIII before it.
For other competitors, selling 10M-15M is already a big deal. LG G2 only sold like 3M and LG is like the #3 most popular OEM in the world behind Samsung and Apple. HTC sold like 5M give or take and that is considered very successful for them considering how bad the One X flopped. Sony sold like 15M Xperia Z's and that is considered very, very successful for them.
Galaxy Notes can sell 10M after a few months and that is considered a niche device that now has broken more into the mainstream. I expect the Note 4 to be the most popular Note ever selling north of 25M.
In the US market, it is a bit different. Apple is the most popular OEM. The gap between iOS vs Android is less than 10% while globally there is a 65% gap between them. In Spain, over 92% of the smartphone users use Android and that isn't exactly a 3rd world country last time I checked. Reason being subsidized pricing since most Americans are in the mercy of carriers. You can get iPhones the cheapest that way unlike most of us who generally have to pay full retail.
Most countries outside US live under a prepaid plan. Heck, I was with AT&T for 10 years when they were still called Cingular. Now I spend $5 every month for my local calls and unlimited texting to the same network.
Alot of us also have two lines with dual sim phones. Alot of us also have multiple phones for backup. My WiFi is free in the mall I live next to so I don't need data and can use Viber or Google Voice to text my relatives Stateside.
North America might be the only continent where Apple/iOS has the biggest presence and where Americans only know 7-8 phone makers. In Asia, it is 25+. Outside US, the gap between Android vs iOS or Samsung vs Apple becomes Grand Canyon wide.