If I have html like this:
This is some text
First span text
It'll need to be something tailored to the needs, which are dependent on the structure you're presented with. For the example you've provided, this works:
$(document).ready(function(){
var $tmp = $('#listItem').children().remove();
$('#listItem').text('').append($tmp);
});
Demo: http://jquery.nodnod.net/cases/2385/run
But it's fairly dependent on the markup being similar to what you posted.