State Health Insurance Assistance Programs (SHIPs). These are state-run programs that can give you free, one-on-one answers to your Medicare questions. Here's the contact information for all SHIP programs.
The official U.S. government web site for people with Medicare
Phone: 800-MEDICARE (800-633-4227)
Social Security Administration
AARP (formerly the American Association of Retired Persons)
BenefitsCheckUp, a service of the National Council on Aging