Comcast has been broadcasting FOX43's HD signal on channel 804 and 234 for some time now. They will be extinguishing the second channel, 234, on January 17, 2011. You will still find WPMT HD on channel 804 with Comcast's HD package.
FOX43 HD is free to receive over the air via antenna on 43.1. FOX43 News in HD will be premiering later this month on 43.1. Keep watching and see the difference!