Apple handheld devices

Apple, in addition to producing Macs, produces portable media players known as iPods. Over time, Apple introduced a mobile operating system known as iOS, and two new devices were produced: the iPad and the iPhone.

iPod (Click Wheel)
iPods with click wheels, which include the iPod classic and older generations of the iPod nano, are portable music players that also have the ability to play videos, display photos, and play games. Sega released one Sonic game for these iPods: a port of the original Sonic the Hedgehog (1991). However, this game is no longer available in iTunes, as Apple has eschewed the availability of iPod games in order to focus on iOS as a gaming platform. If one has already saved a local copy of the game, it can still be synced to an unlimited number of iPods.

The game is compatible with all iPod classics starting with the 5th generation (informally known as the iPod video, due to it being the first iPod with video playback capabilities). It is compatible with the 3rd-5th generations of iPod nanos, but not newer models as they lack physical buttons and instead rely on a touchscreen-based interface that does not support games.

Notably, it is possible to play music from the user's song library in-game, as is the case with many other iPod games.

iPod Touch
The iPod Touch was introduced in 2007 as a low-cost, budget alternative to the iPhone. As it runs iOS, the same operating system as the iPad and iPhone, it can run largely the same apps. Sega has released multiple games for the platform, including many emulated Genesis games and certain original ones, including games from the Sonic series. The iPod touch is currently in the 5th generation, featuring similar technical specifications to the iPad 2/iPhone 4S, but with the taller 4-inch display of the iPhone 5.

iPad
The iPad is a tablet computer. There are two basic model types: one with Wi-Fi capability and one with 3G capabilities, similar to the Playstation Vita. A new, slimmer iPad which also added cameras, the iPad 2, was released in 2011. A third revision was released in March 2012 which features a Retina display and revised internal components, similar to the one seen on the iPhone 4 and subsequent models. This iPad's screen has a higher resolution than a standard 1080p HD monitor. This third generation model was further revised to contain more powerful A6X processors and a Lightning connectivity port, unofficially acknowledged as the 4th generation.

A slightly smaller model that still retains the screen size and aspect ratio is the iPad mini. Released alongside the 4th generation iPad, the iPad mini does not feature a Retina display and uses the same internal components as the iPad 2.

iPhone
The iPhone is a smartphone created by Apple. It was the first iOS device to be introduced (as a result, the earliest versions of iOS were called "iPhone OS"). Unlike the iPod touch and iPad, all generations of the iPhone have at least a built-in camera and a built-in microphone. The iPhone, while very similar in capabitilites to the iPod touch, costs more and features more powerful internal components. The iPhone is currently at the 6th generation, called the iPhone 5.

List of Sonic games on iOS devices
Not all iOS devices are compatible with all of the games listed here. A good prerequisite to playing all of these games would be a 4th-generation iPod touch or newer, original iPad or newer, and an iPhone 4 or newer. However, some games support older devices; for example, Sonic 4 Episode 1 supports devices as old as the iPod touch (2nd generation). The optimal devices for playing Sonic games on iOS (with the best compatibility) seem to be the iPad 2, iPhone 4S, and iPod touch (5th generation).
 * Sonic Spinball
 * Sonic the Hedgehog (formerly an emulation, now a full port similar to the 2011 Sonic CD)
 * Sonic the Hedgehog 2
 * Sonic at the Olympic Winter Games (not available anymore)
 * Sonic the Hedgehog 4: Episode I (HD version for iPad also available)
 * Sonic the Hedgehog 4: Episode II (Demo version available)
 * Sonic CD
 * Sonic & SEGA All-Stars Racing
 * Sonic 20th Anniversary (not available anymore)
 * Sonic Freehand
 * Sonic the Hedgehog 4 Demo
 * Sonic Jump
 * Sonic Dash

Trivia

 * In the iOS version of Sonic the Hedgehog 4: Episode I, Sonic's full speed running animation can only be achieved by running downhill at a very fast speed. This is leftover from the beta version of the game, and it was changed for the console and iPad versions, but left intact in the iPhone/iPod touch version.
 * Presumably due to technical limitations, Sonic the Hedgehog 4: Episode II does not use dynamic shadows in-game. In addition, all cutscenes were recorded from the console version and displayed as pre-rendered videos in the iOS version instead of being rendered in real-time; the cut from the video to stage is especially noticeable in the first act of Sylvania Castle Zone. In the Special Stages, Sonic and Tails' reflection cannot be seen. Instead, their shadows are shown.
 * Older devices, such as the iPod touch (4th generation) and the original iPad, do not display Sonic and Tails' facial emotions. This is most noticeable during the Special Stages, but also during gameplay.
 * Sonic at the Olympic Winter Games has been pulled out of the App Store, as has Sonic 20th Anniversary, though for different reasons.
 * In Sonic the Hedgehog 4: Episode I, Super Sonic's music is replaced by the Invincible theme. The iPod/iPhone version does not have the World Map, while the iPad version's World Map has no animation. The only way to see Episode 1's world map as seen in the console versions is by playing Episode Metal from Episode 2, which does contain the same world map as the console versions.