For Microsoft (MSFT), Windows Phone 7 represents an attempt at righting its serious fumbles in the mobile space. In recent years, as Apple (AAPL) and Google (GOOG) introduced and aggressively updated iOS and Android, Microsoft’s mobile OS fell further and further behind, a reality even CEO Steve Ballmer recently admitted to the press. Now 18 months after development started, Microsoft will spend an estimated $400 million at launch to market its new operating system, Windows Phone 7 [WP7], and get the message out that it’s learned from its mistakes.

Because Microsoft trashed the old system, the WP7 code base is entirely new. That means apps developed for the old Windows Mobile are not compatible. That’s a good thing, offering app makers a fresh start at innovating on the phone, unshackled from legacy code. As of launch, there are a reported 1,000 WP7 apps available, compared to iOS’s 300,000. While Apple’s app ecosystem didn’t grow overnight, WP7 has some catching up to do before it can be fairly compared feature-for-feature and app-for-app with the competition.

But that may not ever be possible. Right now, developers for WP7 are at a bit of a disadvantage when it comes to accessing the phone’s camera, a key piece of hardware that can give apps a big wow factor. Simply put, they can’t use it. Developers are usually provided the necessary tools and documentation for making software for an OS in the form of an SDK, or software development kit, but in this case it appears that Microsoft left out the software hooks necessary to fully control the lens. For app developers, it’s a little like being asked to cook an omelet without a frying pan — it’s probably possible to get the job done, but it’s not going to be pretty.

Two app makers interested in developing for Windows Phone 7, Layar and Fring, told Fortune they can’t access the application programming interface (API) for the camera control in WP7 devices, so it’s a no go for now. Some of the iPhone’s most popular apps, like Layar, Yelp and Trulia, offer augmented reality modes that can show users a live shot of whatever they point their phone at, paired with location based information about the area. But for WP7 users, there’s no augmented reality possible, nor is there, as Fring offers, access to third-party video chatting or perhaps more importantly, the ability to tinker with the camera outside of the phone’s native camera application, to come up with new ways to use it.

“On our side, we don’t really understand what this means or why [Microsoft is] doing this,” Layar’s Maarten Lens-Fitzgerald says, and Microsoft has not given him an explanation.Augmented reality apps actually use not just the camera but the phone’s GPS and compass to pinpoint users’ locations and present their surroundings onscreen with an overlay pointing out info like the nearest bank ATMs, shops, and restaurants. But without camera access, apps like Layar just won’t function.

Jake Levant, Vice President of Marketing for Fring, is excited about Windows Phone 7’s potential but also admits camera access, or lack thereof, is one of the issues currently preventing the company from porting over its popular cross-platform voice and video chat app.

“We need openness,” says Levant. “We need the ability to get to all the different parts of the device. We need to have that freedom. There have been standards set by Android and the like. When the cards are held too tight, it cramps our style and we can’t deliver the value that consumers want and expect from smart phones.”

In response, Microsoft provided Fortune with a statement that said in part, “Windows Phone 7 delivers an all managed code platform in order to provide developers with an easier and faster way to build higher quality and more captivating applications based on the proven and widely adopted Silverlight and XNA Framework technologies.” The statement didn’t dispute that the camera was off-limits.

Levant is quick to point out this precarious situation for some developers is merely a “snapshot in time,” that camera access could come just as quickly to developers via a software update as say, copy-paste and third-party multitasking will come to consumers. For some perspective, Android enabled camera API access to developers from the get-go when it launched in October 2008, while two-and-a-half years passed before Apple did the same with iOS. Indeed, when Yelp’s augmented reality app — the first on the iPhone — was released, it was reported that Yelp actually snuck the feature past Apple, which hadn’t yet officially opened up the camera API in iOS at that time.

It’s possible Microsoft isn’t showing all its cards because those camera tools aren’t fully cooked yet. Or if those tools are ready, Microsoft has another reason for not sharing them. (Could Microsoft be working on its own proprietary FaceTime-like video chat feature?) Unfortunately, deciphering Redmond’s intent from the statement provided to us wasn’t possible, so all we know is that while Apple might’ve had to wait for more powerful hardware and the maturation of its OS to unlock the camera, and second-comer Android was able to unlock it from Day 1, Microsoft was not, some two years after Android, able to follow suit and have a camera API ready on launch.

It’s important to note, again, that Microsoft could release an updated SDK at any time granting camera access, instantly resolving the issue. But the company, three years behind the competition, needs as much developer support as possible as soon as possible. Withholding some of the tools necessary to build a viable app ecosystem at launch, whatever the reason, won’t encourage developers to jump over to Windows Phone 7 anytime soon.

Update: In an additional statement issued after publication, Microsoft clarified its stance with developers. The company provides third-party developers access to the camera for taking photos, but does not dispute the omission of camera video access as required for augmented reality and video chat.