User blog comment:Mobo85/Hot Off The Presses... "Phineas and Ferb Holiday Favorites"/@comment-1858894-20100914175907/@comment-406459-20100918221507

As the producers pointed out at the 2009 Comic-Con panel, Carl technically did get to sing part of one song- the Slushy the Clown jingle. Not much, but then again, Carl probably isn't much of a singer, unlike his voice actor.