After you spend $500 on an iPhone, what will you be able to do with it? Not enough, unless Apple makes it easy for third-party developers to build applications for it. Is Apple doing that? Not yet.

I talked this issue over with Alykhan Jetha, CEO of Marketcircle, a builder of Mac applications in Toronto, while he was in San Francisco staffing the booth at Macworld. "We've asked. They're being tight-lipped about a software development kit for the iPhone. Right now, the answer is no," says Jetha.

Jetha doesn't take that to mean that Apple plans to keep the iPhone application market to itself. On the contrary, he says Apple has been good about sharing a software development kit with third parties to make it easy to develop applications for the Mac OS X.

For example, Marketcircle uses the Mac OS X software development kit's frameworks to build its Daylite productivity, Daylite Mail, and Billings applications for Mac-using professionals. The frameworks speed the developer's ability to interface an application to the networking, user presentation, and calculating capabilities of the Mac.

The iPhone is another OS X device, but it's different than the desktop machine, of course. Developers will need to know how to invoke interfaces to such things as the iPhone's cover flow mode, where the screen orientation shifts from vertical to horizontal, or the iPhone's Maps or Calendar, so their applications can take advantage of these features.

Apple in the past "has been good at offering frameworks that invoke interfaces into its OS X operating systems," says Jetha. "We need a SDK for the iPhone that's similar to the SDK for OS X." The kits allow developers to produce third-party applications that add value to the device that they support.

So before asking where's my $500 iPhone, ask Apple whether your favorite third-party developer has gotten his iPhone SDK yet. That's one way to guarantee your iPhone will have lots of applications to run and be worth its price tag. The iPhone's coming in June. Third-party software development support soon to follow?