The charity will be selected by Twitter pitches - send a tweet to @realhughjackman explaining why your chosen charity is the best. We've found no official deadline for the contest, but Jackman has hinted on Twitter that he may make the announcement on Friday, April 24 on Ryan Seacrest's radio show. (Update: We just got confirmation of this on Ryan Seacrest's Twitter account.)
Jackman's Twitter experience hasn't been without incident: the pledge came a week after Jackman's Twitter feed misspelled "Sydney Harbor [sic]" and incorrectly named one of Australia's most famous landmarks as the "Sydney Opera Center". He explained that the error arose because someone else had ghost-written the Tweet for him, a fact that won't win authenticity points with the Twitter community.
Nonetheless, the campaign will probably have a positive effect: with Jackman encouraging Twitter users to talk about their favorite charities, we might all learn about great causes.