The race began in earnest in March when Steve Jobs unfolded Apple’s “iPhone software roadmap,” a two-part package comprised of a tool kit to help developers write programs for the iPhone and a venue in which to sell them — a variation on Apple’s iTunes music store model called the App Store.

Although the iPhone 3G is set to go on sale in nine days — at 8 a.m. Friday  July 11 — Apple has still not announced when the software store will open. But on Wednesday it delivered a pretty broad hint: a July 7 deadline for developers to submit their finished apps for the store’s grand opening.

“Have your application be among the first available when the App Store goes live,” the notice read. “We will continue to accept applications after this time, however your application may not be available until after the launch of the App Store.”

The message was not lost on developers. From Oracle to VisiCalc, the winning application on any software platform tends to be the one that gets there first — although as VisiCalc proved when it was overtaken first by Lotus 1-2-3 and then by Microsoft Excel, any app can be displaced when a new platform comes along.

According to Apple (AAPL), 25,000 people applied to be part of its iPhone developers program, of which 4,000 were admitted. These include some of the biggest names in software publishing — Sega and Electronic Arts (ERTS), for example — and representatives from approximately 175 Fortune 500 companies, as well as hundreds of one-man shops. But even the biggest boys can use the free publicity that will attend prominent positioning on the App Store shelves on opening day.

With so many apps to choose among, picking winners will not be easy. Apple has the best perspective; it showcased 16 apps at the March SDK event and the June Worldwide Developers Conference (see the keynote here), and by next week it will have seen and signed off on hundreds more.

Meanwhile, pitches from publishers inviting software reviews have started to pour in over the transom. Businessweek last Friday posted a slide show featuring a dozen programs under development (see here). Other journalists have used their blogs to troll for promising apps. The coyest was posted by The New York Times’ David Pogue, author of “iPhone – The Missing Manual,” who may or may not already have an iPhone 3G in hand for review (if he did, he couldn’t say). On Tuesday, he bemoaned the fact that even “Big Chief Newspaper Reviewers” didn’t know what apps were coming down the pike and invited developers to give him sneak peaks (see here). He may have regretted opening the floodgates. By 1:35 that afternoon, his post had been updated and the invitation withdrawn.

UPDATE: The latest version of iPhone OS 2.0 includes a nonfunctioning App Store button on the home screen, according to reviews of a confidential pre-release copy. “Rock-solid,” pronounces Gizmodo’s Jesusdiaz; it “rocks!” says Spark Capital’s bijan sabet.