EA has confirmed a list of hidden characters for NBA Jam.
Beastie Boys
-Mike D
-MCA
-Ad-Rock
Democrats
-President Barack Obama
-Vice President Joe Biden
-Bill Clinton
-Hillary Clinton
-Al Gore
Republicans
-George W. Bush
-Dick Cheney
-Sarah Palin
-John McCain
They did not reveal how to unlock the characters, but I am sure may gamers are trying hard to find out!