All providers and suppliers must begin using the revised ABN starting
September 1, 2008


Beginning Monday, March 3, 2008, providers (including independent
laboratories), physicians, practitioners, and suppliers may use the
revised ABN for all situations where Medicare payment is expected to be
denied. The revised ABN replaces the existing ABN-G (Form CMS-R-131G),
ABN-L (Form CMS-R-131L), and NEMB (Form CMS-20007). CMS will allow a
6-month transition period from the date of implementation for use of the
revised form and instructions. Thus, all providers and suppliers must
begin using the revised ABN (CMS-R-131) no later than September 1, 2008.

http://www.cms.hhs.gov/BNI/02_ABNGABNL.asp#TopOfPage