function insertIntoArray( array:Array, itm, at:uint ):void
{
	var i:uint = 2
	var b:Array = array.slice( 0, at );
	var c:Array = array.slice( at );
	b.push( itm );
	a = b.concat(c);
}
//test
var a:Array = new Array( 0,1,2,3,5,6,7);

insertIntoArray( a, 4, 4 );
trace( a );

Array Function's

array

ActionScript 3