Sprint Nextel Corp. said Thursday that it can't assure that the talks will lead to any transaction, but also confirmed that a deal could involve a "change of control" of the company.
The No. 3 U.S. wireless carrier said it does not plan to give any more details unless it reaches an agreement with Softbank.
Sprint Nextel's stock hit its highest level in a year on Thursday as reports of the talks spread.
The Wall Street Journal, citing an unnamed person with knowledge of the talks, had reported earlier that the potential deal would help Softbank Corp. expand outside of Japan. It put the value of the transaction at more than $12.8 billion.
Sprint had a market capitalization of $15 billion at Wednesday's close, implying that Softbank may not buy the whole company.
Sprint shares rose 85 cents, or 16.9 percent, at $5.89 in morning trading. Earlier, they hit 52-week high of $6.04 per share.
"We would expect to see very little synergies created with such a transaction," said Stifel Nicolaus analyst Christopher King.
Last week, media reports said Sprint's board was considering a bid for MetroPCS Communications Inc. (PCS), the fifth-largest cellphone company in the U.S., to counter an offer by T-Mobile USA, the No. 4. The T-Mobile-MetroPCS deal could make the competitive situation even more difficult for Sprint, which has been losing contract-signing subscribers for years.
Tokyo-based Softbank, once the underdog in Japan's telecom industry, has seen its fortunes improve ever since it started selling the iPhone in 2008. It was initially the only Japanese phone company to offer the iPhone. Rival KDDI Corp. started selling the iPhone late last year.
Shares of MetroPCS dropped 58 cents, or 4.7 percent, to $11.46 in morning trading, as investors speculated that Softbank's interest means there's less of a chance for a counterbid from Sprint.