Item 33 – Enter the provider of service/supplier’s billing name, address, ZIP Code, and telephone number. This is a required field. Item
33a Form CMS-1500 (08-05) – Effective May 23, 2007, and later, you MUST enter the NPI of the billing provider or group. The NPI may be reported on the Form CMS-1500 (08-05) as early as January 1, 2007. This is a required field. Item
33b Form CMS-1500 (08-05) – Enter the ID qualifier 1C followed by one blank space and then the PIN of the billing provider or group. Effective May 23, 2007, and later, 33b is not to be reported. Suppliers billing the DME MAC will use the National Supplier Clearinghouse (NSC) number in this item.
http://www.cms1500claimbilling.com/2011/03/how-to-fill-box-33-on-cms-1500.html