Sprint has told SK Telecom “no thanks” to a proposed $5 billion investment offer, according to a report in today’s Wall Street Journal.

According to the Journal, Sprint has rejected a joint offer from SK Telecom and buyout firm Providence Equity Partners to invest a total of $5 billion in the company. SK Telecom and Providence Equity partners had proposed the investment to Sprint earlier this month in a letter written to the telco in tandem with former Sprint chairman Tim Donahue, said the Journal. In addition to the proposed investment, the Journal also reported that the offer would have installed Donahue as Sprint’s CEO. An SK Telecom spokesman confirmed to Reuters that the company had approached Sprint about an investment offer, but said the company had not yet received an official response from the telco.

A South Korean newspaper first linked SK Telecom with Sprint last summer when it reported that the Korean telco was preparing a bid for its American counterpart. At the time, a representative from SK Telecom’s investor relations department called the report “a groundless rumor” and denied that the company had discussed funding a takeover of Sprint with various global equity funds. SK Telecom, South Korea's leading cell phone carrier, has also invested heavily in Chinese telecom firms, as the company spent roughly $1 billion on bonds last year in China United Telecommunications.

Sprint has been looking for a new CEO ever since its former one, Gary Forsee, stepped down under investor pressure in October. Donahue, Sprint’s would-be CEO in the SK Telecom proposal, retired from the company nearly one year ago. After overseeing Nextel’s merger with Sprint in 2004 as Nextel’s CEO, Donahue spent two years as Sprint’s chairman.

Sprint has faced a wide array of challenges since its merger with Nextel in 2004, from continued difficulties in integrating former Nextel users into the Sprint network to subpar marketing campaigns to investor nervousness over the future of its $5 billion WiMAX investment to a shrinking subscriber base. In the quarter leading up to Forsee’s resignation, for instance, Sprint announced that it had lost 337,000 customers. And a recent report from UBS Investment showed that Sprint’s average revenue per user is falling at a rate of 5% per year, while AT&T and Verizon’s ARPU is growing at an annual clip of 3% to 4%.