HD2/HD3 Channels are located on the FM dial of HD Radio receivers, like this Zune HD, adjacent to traditional stations.
No subscription or additional fees. You will need an HD Radio enabled receiver. Find one here.
Note: HD Radio products receive ALL broadcast radio transmissions, whether they are HD Radio digital signals or traditional analog.
You will need an HD Radio receiver. HD Radio receivers are available in many forms for car, portable and the home. You can select HD Radio receivers from 17 different automakers as factory installed radios and from leading consumer electronics brands at more than 14,000 retail stores across the country. Prices start at $39.
Source: http://www.hdradio.com/what-is-hd-radio, 3/25/2012