Unless Apple changes its rules, Facebook won’t have a Home on iOS Apple's requirements for third-party apps will keep Facebook in its sandbox.

Facebook on iOS will remain a standalone app, at least for now.

Facebook finally unveiled its long-speculated "Facebook phone" on Thursday in the form of the HTC First, but the phone was actually the least important part of the announcement. More importantly, Facebook revealed an entirely new piece of software called Facebook Home that will be available for an array of popular Android handsets next week: Samsung's Galaxy S III, S 4, and Note II, and HTC's One, One X, and One X+. Support for other Android handsets (and, eventually, tablets) will follow in the coming months.

One of the inquiries at the post-event Q&A session asked an obvious question: will Facebook Home support iOS?

"We do have an active dialogue to do more with them but anything that happens with Apple will happen through partnership with them," said Facebook CEO Mark Zuckerberg at the press conference. "Google is aware of what we're doing, but Android is a more open system so we don't have to work directly with them to build this experience."

In short, Apple's phones won't be getting Facebook Home any time soon. If you're familiar with how each operating system works, this should come as no surprise. But if you aren't, a brief explanation may be in order.

“Open” versus “closed”

The word "open" is thrown around by so many people and in so many contexts that it can basically mean anything you want it to mean. In the case of Android and iOS, the distinction is simple: Android's source code is freely available to those who would like to download and tinker with it, and iOS' is not. Android also allows end users to customize things like their keyboard and app launchers, while Apple opts not to in the name of simplicity and consistency.

iOS does allow you to download and run any software you want from Apple's App Store, but even those apps come with restrictions (some obvious and some less so). Third-party apps aren't allowed to communicate directly with one another, for example (you can't use the Facebook app to post a photo stored in Dropbox), and apps can generally only interact with third-party services that Apple explicitly supports (you can post a photo from the Photos app to Twitter or Facebook, but not to Google+).

Finally, third-party apps aren't given the same level of access to the OS as first-party apps: mobile Safari can use Apple's beefed-up Nitro Javascript engine, but Google's Chrome for iOS can't access itor use its own rendering engine (a slower, Nitro-less version of the browser engine is used in it and all third-party apps that load webpages).

Want to change the way your phone looks and acts? You're going to need Android.

Android, on the other hand, lets third parties modify the user experience pretty much however they want—Google has loose requirements for phones that provide access to the Google Play store and the Google Android apps, but otherwise anything goes. Android browsers can use their own rendering engines. The Gallery app can upload photos through any app that tells the Gallery app that it is capable of uploading files (a system called "intents"). Phone makers, carriers, and users can all install basically any application launcher, keyboard, or app that they want.

This is the "open"-ness that Facebook is taking advantage of in order to make Facebook Home work. Home itself is essentially an application launcher that changes the way your phone looks and acts without actually modifying the core Android OS, which will also allow Facebook to keep Home updated without having to clear the updates with a carrier first. Because of how Home works, basically any Android phone can become a Facebook phone as long as it's supported, and the company doesn't have to worry about the fragmentation headaches, vastly different UIs between phones from different manufacturers, and other inconsistencies that plague the platform.

Because of all of this, Home in its current incarnation can't move away from Android to most other platforms, either. Both Windows Phone 8 and BlackBerry 10 have the interfaces and app launchers that they have, and there aren't any mechanisms by which a third-party application could dig its hooks in as deeply as Home does on Android. Without coding a completely separate operating system, then, Android is the only platform that can support Home at all.

Never say never?

Android exclusivity doesn't necessarily doom Facebook Home to failure—Android's worldwide smartphone market share exceeds that of its competition, so the number of potential users out there is high regardless of whether Home comes to iOS or any other platform. It just means that Home as it was shown off today is not a thing that can exist on iOS in the same way that it can exist on Android.

None of that is to say that Home can't evolve or change for iOS, though. Zuckerberg did say that Facebook's relationship with Apple was good, and Apple doesn't have a dog in the social networking fight the way Google does with Google+. The third-party Facebook app for iOS could pick up some of Home's easier-to-port features, and Apple could deepen the native Facebook integration in future versions of iOS (the current level of integration was just introduced in iOS 6, so it could be the first step in a longer journey).

However, Home in its current form simply can't come to iOS (or Windows Phone, or BlackBerry 10) unless Apple drastically changes how it deals with third-party applications. But given that Apple has been bringing many of its existing rules over to its historically more-flexible desktop OS in recent releases (instead of the other way around), we wouldn't count on that happening any time soon.