I live in California, and have done extensive research on this - Sates differ greatly though.
My answer to Health net HMO in So Cal is, yes it does, stating on my contract "when deemed medically...
On a medicare.gov/Publications/Pubs/pdf/10116.pdf, I did not find penile implants listed... check for information on asking about items not listed. Is it medically necessary?
Regular health insurance does not typically cover dental implants. One would need to obtain a separate dental insurance for any dentistry related work.
Medicare is very strict on "medically necessary" procedures. Discuss this with your doctor. Also, check out the new Medicare and You 2009:
http://www.medicare.gov/Publications/Pubs/pdf/10050.pdf