Modifying or replacing the operating system voids the device warranty, communication between apps is limited and controlled, and Apple is the only authorized software vendor.
Hackers have attempted to 'jailbreak' all i OS devices to enable forbidden or unsupported features, such as multitasking in i OS versions before 4.0, themes for the home screen and the use of software Apple has refused to sell such as a battery percentage indicator.
The App Store application, available in all versions of i OS from 2.0 onwards, allows users to browse and download applications from a single online repository (hosted by Apple) with the i Tunes Store.
The i OS SDK allows making applications for the i Phone and i Pod Touch after paying a fee to join the development team.
The developer can then set the price for the applications they develop and will receive 70% of money earned.
With this account one may download music and videos from the i Tunes Store, apps from the App Store, or books from the i Bookstore.
An Apple ID account created without a credit card can be used to get free content, and gift cards can be bought to pay for apps instead of using credit cards.
Jailbreaks for the i Pod Touch first surfaced a month after the first model was released in September 2007, when hackers released Jailbreak Me 1.0 (also called "App Snapp") to jailbreak i Phone OS 1.1.1.
This allowed users to install third-party programs on their devices before Apple permitted this.
From launch, the i Pod Touch was described by journalists as an 'i Phone without the phone', and each i Pod Touch model to date has been introduced with the same release number of i OS as the contemporary i Phone model. Successive updates to i OS since the initial release in 2007 have released additional features.
i Phone OS 2.0, released on July 11, 2008, introduced the App Store, which allowed third-party applications for the first time.
Recent i OS updates have been free for owners of supported i Pod Touch models, but Apple received criticism for charging i Pod Touch owners for versions 2.0 and 3.0, which i Phone owners received for free, and for excluding certain features from the i Pod Touch software that the i Phone included.
Apple's position was that they could add features for free to the i Phone because the revenue from it is accounted for on a subscription basis under accounting rules, rather than as a one time payment.
i Phone OS 3.0, released on June 17, 2009, added features such as cut, copy, and paste, data tethering and push notification support.