estimateShipping

Please see this note about shipping costs.

Method Signature ShippingEstimate[] estimateShipping();
Description
Estimates the shipping for a given cart. This can be used to display all the shipping options that are available to the customer. Typically this is done as a set of radio buttons. Some merchants may choose to set the shipping cost at the lowest one that is available and not give the customer the option of selecting shipping.
Parameters None – the global cart variable is automatically submitted with this call.
Result ShippingEstimate[] – An array of shipping estimates for the given cart. The estimates will be sorted lowest to highest in cost. If the cart contains items that require shipping and this array is empty then an error condition is present.

This is slow. estimateShipping queries all the major shippers live. That takes time. This should be executed asynchronously - via ajax, iframe, etc.