Hint: It was the first generation of the Apple iPhone to have a glass back.
The iPhone 4 was announced on July 7, 2010, at the Apple World Wide Developers Conference. It was the first iPhone ever offered for sale by Verizon, ending Apple's exclusivity deal with AT&T.
It's been the only iPhone model to date that uses the bold color.
The iPhone 5C, available in blue, green, yellow, pink and white, was released in the U.S. on Sept. 20, 2013.
The plasticky, white backing of the phone should be a giveaway.
The third-generation iPhone 3GS, released on June 19, 2009, was the first iPhone to be released in white. It was the also the first model to feature voice controls.
The rear of this phone is silver, with a black band at the bottom.
The original iPhone cost a whopping $600 (with a two-year contract, later reduced to $400) when it launched on June 29, 2007, but that didn't stop people from forming a quarter-mile-long line at Apple's flagship store in NYC to be the first to get it.
The device was revolutionary, of course, but many criticized its lack of 3G connectivity at the time.
Before this, iPhones used larger 30-pin dock connectors.
The phone, released on Sept. 21, 2012, was also Apple's first to have a 4-inch screen.
Hint: It also has a 4-inch screen.
The iPhone SE, released on March 31, 2016, is based on the iPhone 5S design. Unlike the iPhone 5S, however, the iPhone SE is available in the Rose Gold color.
Certainly no other Apple smartphone looks quite like this one.
Hint: Its home button was surrounded by a metallic ring.
This was also the first iPhone model to have a built-in fingerprint scanner.
The presence of Siri on the device is a big hint; this is the first phone she ever appeared on.
Siri was a major selling point of the Apple iPhone 4S, released Oct. 14, 2011.
According to Apple CEO Tim Cook, the "S" in the phone's name stands for Siri.