Level AA is a little more significant, and makes sites accessible to people with a wider range of disabilities, including the most common barriers to use. It won't impact the look and feel of the site as much as Level AAA compliance, though it does include guidance on color contrast and error identification. Most businesses should be aiming for Level AA conformity, and it appears to reflect the level of accessibility the DOJ expects.
The Federal Communications Commission (FCC) enforces regulations covering telecommunication services. Title IV of the ADA covers telephone and television access for people with hearing and speech disabilities. It requires telephone and Internet companies to provide a nationwide system of telecommunications relay services that allow people with hearing and speech disabilities to communicate over the telephone.