you will need to create 4 shipping rules, one for each scenario.
1 item:
Trigger:
Subtotal For Any Column.
If the Subtotal for column "Quantity" is "=" a value of "1"
Calculation:
Flat Rate.
Create a flat rate shipping of $"3"
-----
2 item:
Trigger:
Subtotal For Any Column.
If the Subtotal for column "Quantity" is "=" a value of "2"
Calculation:
Flat Rate.
Create a flat rate shipping of $"5"
-----
3 - 5 item:
Trigger:
Subtotal For Any Column.
If the Subtotal for column "Quantity" is ">=" a value of "3"
AND
Subtotal For Any Column.
If the Subtotal for column "Quantity" is "<=" a value of "5"
Calculation:
Flat Rate.
Create a flat rate shipping of $"11"
-----
6 - 10 item:
Trigger:
Subtotal For Any Column.
If the Subtotal for column "Quantity" is ">=" a value of "6"
AND
Subtotal For Any Column.
If the Subtotal for column "Quantity" is "<=" a value of "10"
Calculation:
Flat Rate.
Create a flat rate shipping of $"13"
To show the error message if there are more then 10 items in the cart, use the following code:
<?php if($yourCartName->TotalColumn("Quantity") > 10) { ?>
Call 123-456-7890 for shipping charges.
<?php } ?>
in the code above, you will need to substitute "yourCartName" for the name of your eCart object.