UPDATED: Online auction company eBay Inc. announced it has agreed to acquire Zong, a direct carrier biller, for approximately $240 million in cash. Zong offers consumers the ability to pay for digital goods by placing the charge on their monthly mobile phone bills.

In the United States, direct carrier billing is important to gaming and social media companies where customers may not have access to credit and debit cards. It's also becoming an important link to basic, secure financial services for the unbanked in developing economies. According to the announcement of the deal, Zong gives eBay, and its payment subsidiary PayPal, connections to more than 250 mobile network operators in 45 countries.

"Commerce is changing," said PayPal President Scott Thompson in the announcement. "With mobile phones, we walk around with a mall in our pockets. PayPal helps to make money work better for customers in this new commerce reality — no matter how they want to pay or what device they're using. We believe that Zong will strengthen this value by helping us reach the more than 4 billion people who have mobile phones, giving them more choice and security when they pay."

PayPal has been active in providing tools to online merchants to make paying on a mobile phone easier for their customers. The company recently launched PayPal for Digital Goods, a product allowing purchases to be transacted in two clicks without leaving a game or content site.

The strategy seems to be paying off. PayPal recently raised its projections for its mobile payment volume to $3 billion for 2011. 

The Zong deal is one of several mobile-related acquisitions for eBay as of late. The company recently acquired start-up Fig Card as well as mobile coupon company WHERE.

(UPDATE: Additional information and links have been added since this was originally posted.)