An iPhone™ app, or application, is what Apple® calls third-party software programs developed specifically for the iPhone™ and the iPod Touch®. The applications available can be downloaded directly by the cell phone, or downloaded to a computer and transferred to the phone. Apple® has an iPhone™ app store for those who want to add new features to their phone. The cost varies, but is generally less than $2 US Dollars (USD) per app.

Those who are interested in any iPhone™ app should make sure they are using an iPhone™. The apps do not work with other types of smartphone hardware. This is different than the situation with iTunes® music files, which can run across several operating systems. Other types of phones will likely have their own specific apps, which are downloaded from a different online store. Many of these applications may be similar to those available on the iPhone&trade, but will not be exactly the same. Features and the interactivity may be slightly different.

An iPhone™ app may provide a number of different functions, depending on the program. Some are meant to show news, sports or weather information. Others are used to provide maps and perhaps even GPS services. The apps can be purely for entertainment, including games, or serve a more practical function. Thus, the marketing model for Apple® includes both the business user and the casual user. This not only includes the list of potential customers, but also gives those customers a broad array of choices.

There are more than two dozen iPhone™ app categories listed in the store where the applications can be downloaded. Some allow the iPhone™ to be turned into a musical instrument. Others will stream live information, or nearly live information, right onto the phone's screen. This is helpful for those who want up-to-the-minute information on stock prices or sports scores. For those who want to be be a little more playful with the phone, there are numerous games to choose from, many with graphics much better than the standard games that come preloaded on many other phones.

Downloading an iPhone™ app requires installing iTunes® onto a computer, or using the phone or iPod® itself. Many may already have the iTunes® application downloaded as it is a popular portal through which to download music legally. The iPhone™ apps are not available directly off the Internet through a traditional Web site. Therefore, those who wish to add new software to their phone will need to get used to the iTunes® interface.