While Clooney is reportedly lobbying for a "Twilight" star to sign on (and E! News reports that Robert Pattinson will step up to host the London segment), plenty of others have answered the call. In addition to appearing on the telethon, Bono and Jay-Z are working on a song to benefit Haiti relief efforts.

U2's guitarist, The Edge, told an Irish radio station that Bono got a call from a producer, Swizz Beats, about the Jay-Z collaboration. Bono settled on an idea during that phone call and then the group "wrote a song, finished, recorded, and sent it back to them," said The Edge. When Bono completed its portion of the song, Swizz Beats posted a TwitPic where he and the U2 singer hold a handmade sign that reads: "One Love Haiti." 

Other recent additions to the official list of celebrities appearing on the telethon include Jennifer Aniston, Brad Pitt, Rihanna, Taylor Swift, Bruce Springsteen, Sandra Bullock, Renee Zellweger and Courteney Cox, Justin Timberlake, Kid Rock, Christina Aguilera and many others will also be lending a hand for the MTV Networks telethon, which airs Friday at 8pm ET/PT and 7pm CT on all major networks and on cable channels such as CNN, BET, MTV, Vh1, CMT and The CW.

Three telethon hosts will broadcast from various international locations: Anderson Cooper will host from Haiti; George Clooney will broadcast from Los Angeles; and Haiti-born Wyclef John will lead the charge in New York City.

Other stars have already given generously. So far, one of the biggest contributions reported is from model Gisele Bundchen, who donated $1.5 million. Variety reports Sandra Bullock, George Clooney, Brad Pitt and Angelina Jolie have also signed $1 million checks to assist the relief efforts.