"NCIS: Los Angeles"'s Chris O’Donnell and LL Cool J do their part to promote service and volunteer as part of EIF's iParticipate national initiative — and ET is behind the scenes as they film a public service announcement encouraging support of military veterans and their families. For more info, check out Iparticipate.org or welcomebackveterans.org. In addition to the "NCIS: Los Angeles" PSA, stars from ABC, CBS, NBC and FOX -- Simon Baker, Emily Deschanel, Eva Longoria Parker, Julia Louis-Dreyfus, Masi Oka, Michael Strahan, Kate Walsh, and Rainn Wilson -- are featured in a 30-second spot, which explains that great change begins with small choices.