I believe they may be purchased at Wal Mart and used without activation for OTA. Be advised that as of the last software rev I was aware of, SD & HD are not output at the same time so you can't record to a DVR while watching SD.
The Portland, OR area has supposedly signed up with them, but before they sell off the extra bandwidth, all the stations are supposed to install newer decoders that will run HD at ~ 12 mbs without degredation. Our local CBS currently uses a good encoder but there is still pixelation with fast motion & whenever a high profile show comes on, like the Grammy's, they switch to full bandwidth allocation and dump the sub channel.