South Korea's SK Telecom has agreed to buy $1 billion worth of convertible bonds in China Unicom's listed arm. China Unicom is the country's second-largest mobile operator that operates both a GSM and CDMA network. Korea's largest operator has voiced its desire to expand beyond its home market for some time into China. The bonds, which can be converted into nearly 9 million shares, would represent a 6.67 percent stake in Unicom. "This strategic alliance will boost China Unicom's CDMA business and give SK Telecom an entryway into the China market," SK Telecom CEO Kim Shin-bae said in a statement. The two have agreed to cooperate on CDMA technology, including handsets, network and value-added services for mobile phones.