The announcement this morning was as low-key as it was stunning. An innocuous posting on Apple’s Hot News page, signed by “Steve” read:

Let me just say it: We want native third party applications on the iPhone, and we plan to have an SDK in developers’ hands in February. We are excited about creating a vibrant third party developer community around the iPhone and enabling hundreds of new applications for our users.

And just like that, one of the biggest criticisms against the iPhone disappeared. Just like that, the iPhone (and to a lesser extent, the iPod touch) has gone from being a pretty but ultimately limited gadget to an extremely exciting handheld computing device. Already blogs are brimming with wishlists for applications on the iPhone, and Mac developers everywhere are salivating over the prospect of finally being able to reach a mass-market audience with their apps.

But (and you knew it was coming...) My main worry lies in this paragraph of Steve’s announcement:

Some companies are already taking action. Nokia, for example, is not allowing any applications to be loaded onto some of their newest phones unless they have a digital signature that can be traced back to a known developer. While this makes such a phone less than “totally open,” we believe it is a step in the right direction. We are working on an advanced system which will offer developers broad access to natively program the iPhone’s amazing software platform while at the same time protecting users from malicious programs.

It seems clear to me that Apple will implement some sort of digital certification process for applications before they will run natively on iPhone or iPod touch. In and of itself, that doesn’t mean much. Most phones (with the notable exception of Windows Mobile devices in most cases) implement such mechanisms. I’m more concerned with how Apple will implement such a mechanism, and how tightly Apple will control it.

It seems likely Apple will charge developers to create applications for the iPhone, either by charging for the SDK itself, or by charging for the certificate the iPhone will require to run the application. But will certificates be issued on a per-application basis, or will developers be able to get a blanket certificate for all their apps? Will Apple handle certification by itself, or will it outsource it to a neutral third-party? Will the certification requirements and process be kept under tightly-guarded NDAs, or will it be transparent and available for any potential developer to review? Will it be cheap? Will the SDK be freely available to anyone (free or paid) or will developers have to enter into some sort of agreement with Apple to get it? Will Apple demand royalties for iPhone apps?

Then there’s the question of the iPhone’s environment for third-party apps. What will apps be able to do on iPhone? Which of its features will be accessible, and which will be off-limits? Will apps be able to access your media library? Your contacts list? Will there be a user-accessible (and user-manageable) filesystem? How will multitasking be handled? Will Apple allow certain apps to have greater access to iPhone features than others, or will it give the user the ability to decide?

Perhaps the biggest question of all is this: Will Apple certify or allow to be certified any app that passes its requirements, even if the app competes with Apple or AT&T’s offerings? If someone builds an alternative media player, will Apple certify it? If someone creates a wireless music download/purchase application to compete with iTunes Wi-Fi, will Apple allow it to run? What about an app that allows iPhone to sync with something other than iTunes on the desktop? Or an app that implements VoIP over Wi-Fi? What about applications of, shall we say, “questionable legality?” SNES emulators, BitTorrent clients, DVD image viewers and so on?

Until these questions are answered, Steve’s announcement is exciting, but it holds no weight. If Apple requires a cumbersome agreement to release the SDK, demands royalty payments, arbitrarily denies certification based on vague or secret criteria and forces apps to run in an environment as highly sandboxed as Safari, then what have we really gained? Not that I think Apple will go that far, but who knows.

What I do know is this: if someone releases a media manager for iPhone that supports Windows Media, DivX and Matroska, and doesn’t require iTunes, I’ll be all over the iPhone like a cheap suit.