How much storage space does the iPhone operating system occupy?

In an article in MacWorld UK, Greg Joswiak, vice president of worldwide iPod marketing, said that the version of OS X that runs on the iPhone would occupy "considerably less" than half a gigabyte (500 MB).

The version of OS X that shipped on the iPhone on June 29, 2007 occupied approximately 300 MB of space.

Are MacOS X "dashboard widgets" the same as iPhone widgets? Can third-party developers create iPhone widgets?

No doubt there are some technical similarities between MacOS X "dashboard widgets" and the "widgets" on the iPhone. Both likely use DashCode.

However, dashboard widgets written for MacOS X are not compatible with the iPhone. Although the company originally forbid all third-party development, on March 6, 2008, Apple released an official iPhone SDK and third-parties began to develop iPhone-compatible widgets as well as applications.

Does the iPhone support Java applications?

Not natively. In fact, in an interview with the New York Times shortly after the introduction of the iPhone, Steve Jobs openly attacked the idea of Java applications on the device, saying "Java's not worth building in. Nobody uses Java anymore. It's this big heavyweight ball and chain."

As as result, as originally published on February 5, 2007, EveryiPod.com speculated that:

With such opposition from Steve Jobs, it is all but certain that the iPhone will never support Java applications or applets.

Nevertheless, when the iPhone SDK was introduced on March 6, 2008, Sun Microsystems announced that the company would develop a Java Virtual Machine for the iPhone, intended to "make sure that the JVM offers the Java applications as much access to the native functionality of the iPhone as possible", and would release it free of charge.

However, questions quickly emerged about whether or not a Java environment would be permitted under Apple's developers terms. By April 24, 2008, Sun continued to express interest in a true runtime environment for Java applications on the phone, but switched gears and started to work with a third-party by the name of Innaworks to merely make it possible to "port Java ME mobile games to iPhone and iPod touch without the need for further manual adjustments".

Since that time, Sun has been quiet regarding Java applications on the iPhone, and although hackers have made progress on "jailbroken" configurations, it seems increasingly unlikely that Sun will be able to support Java on the iPhone. Ultimately, it looks like EveryiPod.com's original conclusion may become the final conclusion.

Can the iPhone run Linux?

Yes. Although no official information is available, creative hackers previously developed a version of Linux for the iPod and are hard at work developing a version of Linux for the iPhone as well.

You may wish to track the development progress of Linux for the iPhone at the FiveForty wiki.