Several sources tell me that Apple is nearing an announcement of some sort regarding third-party development on the iPhone. The bits and pieces I've heard are maddeningly non-specific: I don't know, for instance, whether a full software developer's kit (SDK) will be released; what tier of Apple Developer Connection (ADC) program member you need to be (if any); and how much of the innards will be unleashed. I don't even know whether Apple is announcing that a program is coming, or the program itself.
Those are a lot of unknowns. But what I am hearing from several sources is that the announcement, one that Steve Jobs confirmed without any timetable some weeks ago, will happen soon. Perhaps this week.
Update, 2007-10-16: BusinessWeek reports that their sources say that the SDK won't be revealed until Macworld Expo in January, although some firms may already have been given access, such as game-maker Electronic Arts. It's possible that the SDK has been demonstrated to or discussed with a number of other firms, and that may be what led some of my sources - ostensibly different ones from BusinessWeek - to tip me to a near-term SDK release. Given Leopard's on-time-after-delayed launch, I wouldn't be surprised if the SDK isn't delivered until January.
Update, 2007-10-17: Steve Jobs announces SDK availability in February 2008. See "Third-Party iPhone Developers Idle Your Engines," 2007-10-17.
How It Could Work -- What developers want from Apple is the same kind of environment provided for creating software under Mac OS X: Integration with Xcode, the programming environment that the company maintains made it simple to move programs from the PowerPC to Intel architecture because of its flexibility and independence from processor-specific constraints.
If Apple simply inserted an iPhone framework into Xcode, so that developers could work with tools they already had, with the limitations imposed on what the iPhone could do, you'd see applications released in minutes. It's likely that Apple won't release a full-fledged environment in the early days, but something more modest that will still take advantage of developers' (and Apple's) investment in the Xcode system.
Related to this, however, is whether Apple and AT&T will require certification of programs before they run - all programs, or perhaps just ones that use certain iPhone features. Research in Motion requires certification for programs running on the Blackberry that access features like dialing, but I'm told that process isn't onerous, and it's part of the approach that RIM has used to great success in penetrating government and high-security businesses.
The other smartphone platforms - Palm OS, Symbian, and Windows Mobile - generally allow any arbitrary program to be installed, but access to phone features is typically limited, and network access is sometimes restricted to Wi-Fi, when that's available. This limits a cellular carrier's (and a user's) exposure to a phone sucking huge amounts of cell network bandwidth due to a third-party application.
Apple could pull a neat trick by allowing programs that want to access only Wi-Fi network features to operate in an unlimited fashion; if EDGE service is desired, then a program needs to be registered and certified, and be a good network customer. There could even be a revenue requirement or split to make those kinds of applications work in AT&T's model.
This speculation stems from the fact that the iTunes Wi-Fi Music Store works only over Wi-Fi, as a fer-instance. The same structure that allows that program to limit its data access to a specific network medium might be available as part of a larger controlling structure.
We'll see if my sources are right. This could assuage the feelings of many of us who knew that our unsupported applications were, you know, unsupported - read John Gruber's amusing essay on "The 'Un' in 'Unsupported'" - but still liked to have access to stuff beyond that which Apple provides.
Web Applications List -- After first posting this article, I discovered that 9to5Mac had published a piece earlier in the day about Apple accidentally revealing a page devoted to third-party Web applications that could be installed on an iPhone, if I understand the article correctly. In contrast, my sources have been talking about real native iPhone applications, not Web applications.
In fact, Apple took the Web applications page live on 11-Oct-07, and it is merely a directory of Web-based applications designed for the iPhone, not applications (browser-based or native) that can be installed. The directory itself displays fine on an iPhone, but isn't really optimized for it, which is a sort of twisted idea on Apple's part.