create a rul on the shipping tab far each quatity break, for example, the first rule woulld be:
Triggers:
Subtotal for any column:
If the subtotal of Column [Quantity] is [>] a value of [0]
AND
Subtotal for any column:
If the subtotal of Column [Quantity] is [<=] a value of [5]
Calculation:
Flat rate of 2.49
to display the please call error, you would need to add code to the page:
<?php if($<your cart name>->TotalColumn("Quantity") >= 500) echo("Please call"); ?>
where <your cart name> is the name of your ecart object.