On the plan’s website—Visit the drug plan company’s website. You may be able to join online.
On Medicare’s website—Join a drug plan at www.medicare.gov on the web using Medicare’s online enrollment center.By calling 1-800-MEDICARE—Call 1-800-MEDICARE (1-800-633-4227; TTY 1-877-486-2048) and talk to a Medicare customer service representative.
(Source: Social Security Administration: Understanding The Extra Help With Your Medicare Prescription Drug Plan publication 10508, January 2011. Additional examples and links from Q1Group LLC)