With Apple’s introduction of an iPhone Software Development Kit (SDK) last week, it seems everyone and their brother is hopping on the iPhone bandwagon or considering the jump. There are still some issues about software distribution to be worked through, however—particularly when it comes to shareware.

Just to recap last week’s happenings, Apple plans a June release for the iPhone 2.0 software, which will include new features and capabilities including an App Store—a way for users to buy and download software for their iPhone. With the possible exception of enterprise users downloading software needed by their companies, this will be the one way for iPhone users to get legitimate software for their system.

In announcing the App Store, Steve Jobs gave some basic information about how distribution will work—developers will be charged 30 percent off the top for the privilege of distributing their works through the App Store, and Apple will pay them monthly for the services they provide. Apple will also vet software to make sure it doesn’t present a security risk, contain pornography, or hog excessive amounts of bandwidth. The App Store will also distribute free iPhone applications (provided their developers pay $99 to join the iPhone Developer Program).

What Apple didn’t detail, and what’s missing from the documentation provided with the SDK, according to the developers I’ve spoken with, is any mention of how to distribute trialware or shareware software for the iPhone. Here’s what we’ve managed to piece together for our iPhone Software FAQ:

We assume Apple won’t let you sell a “free” program that requires an unlock code. However, there are some other scenarios we expect to see. First, donationware: People will probably sell “free” programs that request that you make a donation if you want to keep the project going. We don’t think Apple will have any problem with that, since the donation would be voluntary. Second, it’s possible that you’ll see two versions of various iPhone programs: a free “lite” version that’s a good advertisement for a more feature-rich for-pay version.

Then there are programs such as the Iconfactory’s Twitterrific, a Mac program that is free, but contains ads. For an “upgrade” fee, users can shut off the ads. Whether Apple would allow this to be handled within the program or there would need to be two separate versions of an iPhone version of Twitterrific remains to be seen.

That’s a fair amount of guesswork, with nothing definitive on the subject from Apple. And the absence of detail has some shareware makers wondering whether they’ll be able to get their software to iPhone users in the manner of conventional shareware.

Mac and PC users alike have grown accustomed to being able to download versions of shareware that they can try before they buy. These applications are usually either feature-limited or time-limited—that is to say that they’ll stop working after a set number of days once they’re activated.

The same situation exists for some cell phone software, which may be available for download through a carrier’s Web site and may operate for a set number of hours or days before you have to pay for it. The basic groundwork for that would seem to have been set already with Apple’s FairPlay DRM, which is now being used to offer time-limited video rentals through the iTunes Store. How iPhone software developers would enable that to work is still anyone’s guess, however, as Apple hasn’t documented that capability or exposed it in the beta SDK it released to developers.

Another possibility according to a couple of developers I spoke with is that they will need to release two versions of their applications—one that’s feature-limited, as a free demo, and another full version for paying customers. That might ultimately too cumbersome for some customers to bear, though, as it’d require them to download the same program twice.

Another issue arises with beta software. It’s common for some shareware makers to issue pre-release beta versions of their software to let early adopters iron out kinks and to help get feedback on new features and interface designs. Will Apple allow beta software to be distributed through the App Store? It’s another question that has developers scratching their heads at this early stage in the game.

We’re still a ways off from the June launch date for the App Store. And developers are just now rolling up their sleeves and taking a look at the iPhone SDK to determine what they can and can’t do. So there’s a long row to hoe between now and then, but it doesn’t mean that developers aren’t asking good questions—questions that Apple will need to answer in order for some iPhone projects to see the light of day.

Note: This blog first appeared on our sister site Macworld.com