The 4-state barcode is also known as OneCode or 4-CB. The “state” in the title does not refer to geographic states, but rather the lines that make up the barcode itself, referring to the four distinct vertical bar types used.
As far as DAT-MAIL and Post Master Confirm users go, your software is already configured to be able to use the data from the new barcode for Confirm uploads, so you will be able to participate in the new One Code Confirm services offered as soon as the USPS is ready. Implementation by the USPS for all letter classes with OneCode Confirm is September 1, 2006. Flats are expected to be able to use OneCode by Spring of 2007.
For detailed information on the 4-State Barcode, refer to the USPS’ RIBBS site here