What applications are available for the iPhone? Will third-party applications be available in the future?

Please note that there now are thousands of third-party applications available for the iPhone. Originally, Apple refused to allow third-parties to develop applications and this Q&A remains for "historical" interest.

When introduced on January 9, 2007, Apple demonstrated that the iPhone includes programs that provide iPod, phone, and "Internet communication" functionality. On January 15, 2008, Apple introduced a handful of new applications for the iPhone, provided for existing iPhone users at no additional charge.

For iPod functionality, the iPhone includes software for accessing music, video, and photo content. For phone functionality, the iPhone includes software to make and receive phone calls, manage a directory of contacts, retrieve voicemails in any order just like e-mail -- dubbed "Visual Voicemail" -- an SMS application for text messaging (updated on January 15, 2008 to support multiple recipients), and a photo management application that Apple professes "goes far beyond anything on a phone today". On January 15, 2008, Apple also added a new software program that makes it possible to view movies rented via an Apple TV on the iPhone.

As an "Internet communication" device, the iPhone has an "advanced Safari browser" that allows one to view entire webpages as designed for a computer and zoom in to read content by tapping and "pinching" on the multi-touch display. It also has an HTML capable e-mail client that fetches e-mail in the background over POP3 and IMAP, a calendar, and "Widgets". Initially, widgets provided access to Google Maps as well as weather and stock feeds, but on January 15, 2008, Apple introduced a new Maps application that automatically triangulates ones position using nearby wi-fi base stations and cellular towers to make it easier to find places of interest. Apple additionally unveiled a version of the "Web Clips" functionality from the desktop version of MacOS X that makes it possible to "clip out" portions of a website and these "clippings" will be automatically updated as the website is updated.

On October 17, 2007, Apple reversed the foolish decision to not allow third-party development and promised an official SDK in February 2008. The SDK was released on March 6, 2008 and developers immediately went to work on third-party programs. For more information on the original SDK, you may be interested in reading an article from the always excellent TidBITS.

To read the full history that led to the formal development of third-party applications -- including info on various hacks for using third-party applications prior to Apple's approval -- feel free to read the below in-depth answer.

To the disappointment of many in January 2007, Apple said that the company was not going to allow third parties to develop applications for the iPhone.

Reporting for the always excellent MacInTouch, Henry Norr said that:

Apple spokespeople wouldn't say yesterday [January 10, 2007] what components and features of the Mac OS will be running on the iPhone; they did say that the phone is a "closed platform" and that they are not offering Mac application developers any tools to bring their programs to it.

Gizmodo also reported that Apple Vice President of Applications, Eddie Cue, and Senior Vice President of Worldwide Marketing, Phil Schiller, informed the blog that the iPhone "won't be an open system that people can develop for".

Perhaps most damning, in an interview with the New York Times, Steve Jobs himself said:

You don't want your phone to be like a PC. The last thing you want is to have loaded three apps on your phone and then you go to make a call and it doesn't work anymore. These are more like iPods than they are like computers.

These are devices that need to work, and you can't do that if you load any software on them. That doesn't mean there's not going to be software to buy that you can load on them coming from us. It doesn't mean we have to write it all, but it means it has to be more of a controlled environment.

As the iPod is a "closed platform", and Steve Jobs himself was in opposition in January 2007, it seemed doubtful that Apple would allow open third-party iPhone software development. However, EveryiPod.com was hopeful that Apple would at least contract some third-party application development (like the company did for games with the iPod).

On May 10, 2007, in the annual meeting with Apple shareholders, Steve Jobs said that the company was "wrestling with" the decision of whether or not to allow third-parties to create iPhone software, which made some cautiously optimistic regarding future development.

On June 11, 2007, Apple announced that the iPhone would "support third-party Web 2.0 applications" and that:

Developers can create Web 2.0 applications which look and behave just like the applications built into iPhone, and which can seamlessly access iPhone’s services, including making a phone call, sending an email and displaying a location in Google Maps.

Engadget may have summarized this decision the best with "weeeeeaaaak." There was not a developers kit released at the time.

This announcement might have been enough to fool the popular press into believing that Apple had "let independent developers write applications" for the iPhone, but savvy readers no doubt recognized the substantial difference between simple "Web 2.0 applications" that run in a web browser and "real desktop applications" like Skype.

When the iPhone Q&A was first published on February 5, 2007, EveryiPod.com commented:

Regardless of Apple's intentions, it seems probable that creative hackers eventually will bypass restrictions and develop some iPhone "OS X" applications without Apple's blessing. Additionally, programmers no doubt will churn out a version of Linux optimized for the iPhone complete with compatible applications.

As soon as the iPhone was released, diligent hackers started working to develop third-party applications and on July 19, 2007, as first spotted by Engadget, the iPhone Dev Wiki announced a "Hello World" application. This basic example opened a crack in the door for the "unofficial" development to begin. Since that time, individuals wrote software to manage accounts, emulate the NES console for games, and many more.

At first installing applications was challenging, but the hardworking people of Nullriver released an installer application that made it much easier. On September 27, 2007 Apple released a software update that disabled third-party applications, but creative hackers immediately got to work breaking the patch and were able to do so by October 9, 2007. A subsequently released web-based tool called AppSnapp made the process extremely easy -- simply accessing the website with an iPhone would crack it for third-party apps.

Perhaps prompted by users and hackers who wanted to run additional applications, on October 17, 2007, Apple reversed the foolish decision to not allow third-party development and promised an official SDK in February 2008 (it was released on March 6, 2008). Regardless, on October 27, 2007, Apple pledged that future updates will "most likely break" unofficial third-party applications. Sure enough, Apple released another patch to disable third-party apps on November 9, 2007 -- with the launch of the iPhone in continental Europe -- and this was hacked essentially immediately.

Even after the release of the official developer's SDK, on March 12, 2008, hackers managed to crack the 2.0 version of the iPhone software -- months before it's formal release -- to support essentially all unofficial third-party applications whether they are distributed through Apple's "App Store" or otherwise and the battle between official and unofficial application access no doubt will continue.

Regardless, with a formal developer's program in place, iPhone enthusiasts can look forward to many great applications that substantially expand the functionality and usability of the iPhone.