Medicare's annual open enrollment is from Nov. 15 - Dec. 31. During this time, Medicare beneficiaries may change to Medicare Advantage plans, return to original Medicare or change prescription drug plans. Changes take effect on January 1, 2010. If you enroll in or switch to Medicare Part A and want Medicare Part B coverage, you can enroll between January 1 and March 31, with enrollment effective on July 1... [1013 word article, November 2009]