Either the new iPhone SDK ain't all that easy to use, developers with PCs want to build some iPhone apps or hackers just want to have fun, because Silicon Alley Insider reports that the new book from O'Reilly, "iPhone Open Application Development," is already sold out on Amazon.com.

The book, which just went on sale this month, is the top-selling book in Amazon's PC section and third among Mac books, the article says. Its overall rank is 1,694.

All About Symbian reports that Nokia has opened the beta for Widsets 2.0, allowing developers to download and work with the new version. Widsets are these nifty mobile widgets that make it possible to get Web content onto a mobile phone.

According to the post, new features include "better integration between Widsets and the rest of the device, including the ability to initiate a phone call or open a browser window." It says the new version also loads faster and results in widgets that look more "polished."

The Web site has a number of pictures demonstrating the new features.

Google's Mark Crady, the engineering manager of Google Maps for mobile, has a post on the company's official Mobile Blog with tips on making it easy to launch your favorite mobile apps.

The post details how to find the oft-hidden ability to program "convenience keys" on a phone in order to launch an application by hitting just that key. He also posted cheats on how to configure the keys on the BlackBerry, Samsung BlackJack and Nokia N95, and included a video for folks who work better following along than by following written instructions.

Do you feel lost if you leave the house without your cell phone? Have you sent a text message or e-mail from your BlackBerry at night or on the weekend recently? Do you use your wireless device at home instead of your landline phone? If so, you might suffer from disconnect anxiety.

Ars Technica writes about the results of a study from Solutions Research Group whose finding show that 27% of us experience increased stress levels when we're away from our cell phone or the Internet. The study also claims that an additional 41% of us occasionally feel anxious when cut off from our mobile or online communications lifelines.

Reportedly, folks under 50 are more likely to be affected with the malady, which is said to present differently for different generations.

Click continued to take SRG's survey and see if you're afflicted.

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If you've ever wanted to take time off from work to go to the circus, now's your chance to join the crowds at the first ever Mediabistro Circus. The first-of-its-kind event, May 20-21 at New York's Skyline Studios, is a two-day "unconventional gathering of creative content producers geared toward senior-level professionals."

Session topics include mobile technology, online video, social networking, blogging, digital publishing and user experience design.

You can register, see the list of speakers and get other official info on the Mediabistro Circus Web site and then check out the blog to fill the void until the Circus comes to town in May.

If having a healthier heart isn't enough to get you up and walking, maybe being able to charge your cell phone or PDA while out and about will do it.

Researchers from the University of Michigan, University of Pittsburgh and Simon Fraser University in Canada have developed a new type of knee brace that harvests the kinetic energy produced from walking and turns it into a different kind of energy that can be used to power cell phones and other portable electronics devices. There are also more scientific uses for the energy, such as powering prosthetics or neurotransmitter implants.

An article on the Discovery news site goes into the details of how it all works.

CNET's The Cheapskate blog points out a cool feature that online storage site drop.io just added to its offerings: free MP3 recordings via cell phone:

"Now, when you create a drop, you get a phone number and special extension," blogger Rick Broida reports. "Just dial in from your cell phone (or any phone), enter the extension, and start talking. When you're done, drop.io turns the recording into an MP3 you can play, share, download, or whatever."

From there, you could do whatever you want with it, such as use it for reminders, record a lecture, work on a podcast, or even use it to record interviews, Broida suggests. This isn't necessarily mobile-media related but we thought it was worth mentioning, since it seems pretty useful.

Record free, unlimited MP3 audio with your cell phone [The Cheapskate]