South Korea's largest mobile phone operator SK Telecom Co will buy as much as US$1 billion in bonds from China Unicom that can be converted into a 6.7% stake in the company, Bloomberg reported. The Korean group said it wanted to generate overseas earnings to make up for a slowdown in subscriber growth in its domestic market, following a similar strategy to the one used by Singapore Telecommunications. The investment will enable China Unicom to upgrade its networks ahead of the long-awaited implementation of 3G services. China Unicom is currently vying with larger rival China Mobile and fixed-line operators China Telecom and China Netcom for 3G licenses. SK Telecom and China Unicom already have a US$6 million joint venture offering wireless content such as games and ring tones, which was set up in 2004.