While visiting Japan in September, 26-year-old Stanford graduate Eddie Kim picked up a book about coding Android apps because he thought it might be a fun hobby. Little did he know that six months later, his casual creation would earn him more money than any of his full-time jobs.

Kim, a former Volkswagen engineer and co-founder of San Francisco-based startup Picwing, now earns $13,000 each month off an Android app called Car Locator (right), which helps users find their parked cars. Kim’s app, which he sells for $4 per download, took him only three weeks to code.

“I thought about making an app for the iPhone, but my thoughts were, it’s such a crowded space right now, and I thought Android would be a better opportunity to get involved in,” Kim told Wired.com.

“Plus, I learned that you need a Mac to do iPhone development, and at that point I lost all interest,” said Kim, a proud Windows user.

Kim’s success story is the first we’ve heard from an independent coder developing for the Android platform. While the iTunes App Store was still just months old, we saw a handful of reports about independent developers making copious amounts of money off their iPhone apps. For example, independent coder Steve Demeter said he made $250,000 in profit in just two months with his iPhone game Trism. Later, programmer Ethan Nicholas raked in $600,000 in a single month with hot sales of his game iShoot, and he immediately quit his job. Because of these success stories, many technology observers have deemed the mobile app opportunity a digital gold rush.

Google’s Android Market, which opened in October 2008, has been around almost as long as the iPhone’s App Store. But only in recent months, with the introduction of the Motorola Droid and Google’s Nexus One, has the Android platform been gaining serious momentum. In February, Google announced that 60,000 Android phones are shipped each day.

Still, stifling Android developers is the lack of a simple market for third-party apps. Google doesn’t own a prominent platform for distributing apps, as Apple does with iTunes. And some developers have shied away from the Android platform in fear of fragmentation — having to develop and support several versions of the same app for various different phones from several manufacturers. By comparison, the iPhone offers a relatively clear-cut audience of 75 million iPhone and iPod Touch customers, with smaller differences in features between the various models. (Though the advent of the iPad, with its larger screen, may complicate Apple’s market further.)

Citing Google’s weaknesses, Gameloft, a major game company, said in November 2009 that it was significantly cutting back its investment in Android.

“It is not as neatly done as on the iPhone,” said Alexandre de Rochefort, Gameloft’s finance director, during an investor conference. “Google has not been very good to entice customers to actually buy products. On Android, nobody is making significant revenue…. We are selling 400 times more games on iPhone than on Android.”

Against that background, Kim’s success story is all the more impressive.

So what exactly did Kim do to rake in some serious dough? First, he employed a “freemium” strategy, offering a free version of Car Locator for users to try out, in addition to the paid version of the app, for which he charged $2 at first. Kim’s sales started out small, netting an average of about $80 to $100 per day. Then, his app became featured in the Android Marketplace, at which point Car Locator began netting an average of $435 per day. Kim then gradually raised the price to $3, and then to $4, and surprisingly, sales grew even stronger. (Kim illustrated his progress in the chart below).

What’s more, Kim doesn’t find developing for Android particularly difficult. He said the concerns about fragmentation are overplayed: There are currently four different versions of Android, and it’s not hard to account for a few variations of the same app.

“It’s not a huge pain in the butt for developers right now,” Kim said.

At this rate, Kim is set to earn a six-figure yearly income. But he said he doesn’t plan to quit his job or start churning out Android apps. After all, luck was a big factor in helping Kim’s app succeed, just like it was for Demeter and Nicholas. (In an interview with Newsweek, Demeter says he only really struck it rich after investing his App Store earnings in the stock market. Nicholas hasn’t come out with a big hit like iShoot ever since, and he told Newsweek he’s “very worried about being a one-hit wonder.”)

For now, Kim hopes to ride on Car Locator’s success for as long as he can.

“Just from last month’s sales, it’s making more money than when I was employed as an engineer at Volkswagen, though I’m not sure how long it will last,” Kim said.

Photos: Jon Snyder/Wired.com