Warren Buffett said Wednesday that 40 of the world’s wealthiest people have joined him and Bill and Melinda Gates in pledging to give away at least half of their personal fortunes to charity.

In a conference call with reporters, Buffett said he and the Gateses had called between 70 and 80 of the people listed on the Forbes list of the 400 wealthiest people in the world to make the appeal that they call the “Giving Pledge.”

“It was a very soft sell,” said Buffett, who in 2006 promised to give nearly all of his fortune away, mostly to the Bill & Melinda Gates Foundation of Seattle.

Those who have signed the pledge include Microsoft co-founder Paul Allen (who previously said he would donate his fortune), Oracle CEO Larry Ellison and producer/director George Lucas. For a full list and details on most of the donors, you can go here.

Buffett said he and the Gateses plan to continue their direct appeals, and that others who have made the pledge will also help the fundraising effort. Over the next few months, the group of donors will organize several dinner meetings around the country to convene and recruit others to join them.

Later this year, Bill Gates and Buffett will take their appeal outside the U.S. In September, the two friends will go to China to meet with a “large group of wealthy people,” then will take a trip to India in March, Buffett said.

I didn’t get a chance during my conference call to ask my question about whether Buffett plans to donate any funds to nonprofits, advocacy groups or think tanks that will help support the appeal. But it appears that is already happening.

According to the Gates Foundation website, it awarded a three-year, $675,000 grant in July to the Massachusetts-based Zing Foundation Inc. to “build existing capacity to encourage a broad spectrum of people to give more boldly.” The effort, which is being called Bolder Giving, is aimed at getting all people to donate large portions of their wealth to charity.

Already the strategy is in action. About an hour and a half after the conference call wrapped up, Bolder Giving issued a news release lauding the Giving Pledge.