Apple iPhone 3GS for sale right now on eBay
Apple has sold 1.1 BILLION iOS devices in the world. Add in the 125 million iOS driven iPod touces that were not counted by The Motley Fool, and the number becomes more than 1.225 Billion. Over 700,000,000 of that 1.225 Billioon are later model iPhones. Why do you then have a problem with believing that 100,000,000 of them are being used in the United States, Apple's home and primary market where the iPhone has been on sale for over 8 years? This number comports quite well with the percentage of iPhone users being reported by the carriers.
"(Apple) iPhones captured 44.2% market share among U.S. smartphone subscribers aged 13 and older based on a three-month average ending July 2015, an increase of 1.1 percentage points over the preceding three month average. -- Sep 3, 2015
Source comScore
Wikipedia lists that there are 327,577,529 cellular phones in use in the United States. 44.2% of those should be Apple iPhones according to the statistics reported by the carriers. However, a lot of those cellular phones in use are still dumb flip phones or plain candy bar phones. . . that's estimated to be somewhere around 65,000,000, so let's subtract those dumb phones from the 327,577,529 - 65,000,000 = 262,577,529. 44.2% of that number of smarter phones is ~116,000,000. Ergo, Sgt. Dave, 100 million Apple iPhones is not out of the question, in fact, it is a low estimate. Heck, Sarge, Apple sold 48.6 MILLION iPhones in just the last quarter alone!
In addition, Apple iPhones hold their value far longer than do any other cellular phones. You find this astounding? Why? They are still useful and in demand by consumers far longer than others that simply do not last as long. Otherwise, Sarge, why would Amazon be even be thinking they could sell a six year old iPhone which does not even have 4G technology for that much money????