I have the same problem. When I try to call someone or when they call me, we both sound like aliens. I used the Yahoo 7.0 Beta and voice worked great! As soon as we upgraded, the Yahoo! Call (Voice) feature no longer works.
Yahoo says it could be bandwidth, time of day, or region. Well, sounds bogus to me. Previously, on the Beta version, it worked any time of day, to any region, and the bandwidth was, and still is, DSL.
Immediately after the upgrade from Beta to the “official” 7.0 version, the feature stopped working.
I have uninstalled and reinstalled numerous times. Don’t know what else to do. Any ideas?