NEW YORK (Reuters) - Microsoft Corp on Monday said it would be willing to reopen talks to buy all or part of Yahoo Inc -- but only if a new Yahoo board is elected, a major boost for investor Carl Icahn's board slate.

Microsoft, which broke off months-long talks in early May to buy the Internet company for $47.5 billion, said it would resume discussions immediately if a new board were elected at Yahoo's August 1 stockholder meeting.

The Microsoft statement came after Icahn, the billionaire financier who holds over 4 percent of Yahoo, issued an open letter saying he had "spoken frequently" to Microsoft CEO Steve Ballmer over the last week. Previously, the two had not spoken.

"This is the first concrete confirmation we have that Microsoft is willing to come back to the table," said UBS analyst Ben Schachter. "It gives Icahn a much stronger hand going into the shareholder vote. It significantly raises his profile and his likelihood for success."

Ballmer told Icahn that a big impediment to any Yahoo deal was his concern that the current board could "mismanage" the company while the deal awaits regulatory approval, a process that could take nine months or more, according to Icahn.

In an interview, Icahn argued that his proposed dissident board slate would make Microsoft feel more secure in risking a large sum of capital to complete the deal during the regulatory approval process.

"You don't have to be Sherlock Holmes to realize there is no great comfort zone between the current Yahoo board and Microsoft," said Icahn. "During this waiting period for regulatory approval, any acquirer -- not just Microsoft -- would want a steward they would feel comfortable with."