Amazon.com (NSDQ: AMZN) is making a significant move into mobile today that puts it in direct competition with Apple’s iTunes and eBay’s PayPal. The announcement also provides a hint as to where the Seattle-based company is headed next: mobile content and applications. 

Up until now, Amazon has only experimented in mobile, by releasing a few shopping and MP3 applications. But today, Handmark, a mobile content and storefront company, said it is integrating Amazon into its mobile storefronts, allowing users to pay for content and applications using their credit card on file with Amazon. Handmark’s VP of Marketing, Evan Conway told mocoNews: “We have a variety of payment methods, but this is a big deal for both companies. It’s nice to be selected for Amazon’s first one [partnership].”

The move puts Amazon more in direct competition to iTunes and PayPal, especially since Amazon could easily start selling Handmark’s expansive mobile content and applications catalog online, where it reaches millions of consumers. Apple (NSDQ: AAPL) has already demonstrated how big of an opportunity it is. Apple has 85,000 applications available and has achieved two billion downloads from the 50 million iPhone and iPod Touch owners worldwide. But Amazon can target a much bigger market. Rather than focusing on one phone, its solution could work across many networks or phones.

Conway said Amazon’s payment system will be integrated into all of Handmark’s 50-or-so mobile storefronts around the world, including stores on the Windows Mobile and BlackBerry platforms. “It will be out almost instantly,” he said. Handmark already has a number of payment solutions, including carrier billing, credit cards and PayPal. But the big hurdle for consumers is often convenience. If it’s not easy, they move on. Carrier billing is presumed to be the best solution because users never have to enter any information to make a purchase. Conway said with Amazon’s payment solution, users will enter their Amazon username and password and then enable one-click purchasing after that. “This will bring in a whole group of folks who have their credit card on file with Amazon to have a seamless approach.”

However, Amazon is not the only one competing for this market. When you look at the players that have access to consumer credit in mobile, it’s not just the carriers. PayPal has also signed a partnership with Research In Motion to power the billing platform for BlackBerry’s App World. It’s not clear which provider has the biggest reach. Recently, Apple’s Steve Jobs said iTunes has 100 million credit cards on file. PayPal has about 68.6 million registered active accounts, according to a 2008 SEC document, and Amazon declined to discuss how many users’ credit cards it had on file. Others vying for this space include Google’s Checkout.

To be sure, the opportunity is large. Whichever company is able to crack the market first, it will not only get a cut of mobile purchases, but may lead to more business down the road. Virtual goods is only the beginning. Next may be buying physical goods at the point of purchase, which has yet to take off in the U.S.