Last week's demos of killer games and other third-party apps for the iPhone were eye-popping, all right. But after a few days poking around the just-released beta of the iPhone software kit, developers say they're finding some troubling limitations.

Among them: third-party iPhone apps will not—according to Apple's developer guidelines, at least—be allowed to run in the background, as do the standard iPhone applications (such as Mail, Safari, and so on).

Now, that's not such a big deal when it comes to, say, games or tip calculators, and it will certainly help to avoid the memory leaks that plague some Windows Mobile phones.

However, the rule could pose a problem for programs like instant messenging apps (like the long-awaited version of AIM for the iPhone), which typically run in the background to receive and alert you to incoming messages.

Another potential problem: the iPhone SDK states that "[a]n Application may not itself install or launch other executable code by any means, including with limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise."

Translation: Programs like Firefox and Opera, which (as Wired notes) support plug-ins created by users, might be barred from the iPhone, or forced to shed some of their coolest features.

That said, developers are still working their way through the intricacies of the iPhone software kit, and it's not clear how stringent Apple (which will be the "gatekeeper" for any and all third-party iPhone apps) will be in enforcing the various SDK guidelines. Indeed, Cupertino may well make some exceptions, especially for the high-profile version of AIM for the iPhone. Or at least, let's hope so.

Related:
Apple kills third-party background processes on iPhone [PhoneMag]
Has Apple Banned Firefox From the iPhone? [Wired]