Last year (2008), WLTW-FM 106.7 in New York USA, started playing all Christmas on three of their HD Radio channels during the second week of October.
WLTW New York with listen links to all programming - http://www.1067litefm.com/cc-common/hdradio/
There seems to be a national (U.S.) set of HD radio station programming to which radio stations may subscribe and broadcast over local HD channels. Chances are that other stations subscribed to the same source as WLTW will carry the same programming. If you have a HD radio receiver, start digging and report your Christmas findings!