Every device maker has its own schedule for releasing updates. TomTom and Magellan often release map updates with general software updates, which can occur a few times a year. Garmin releases map updates separately from program or firmware ones. Navteq, the company that creates the mapping information used in most devices, releases quarterly updates. The price varies as well. The Garmin North America DVD currently goes for $150, and a TomTom upgrade CD costs $50. Of course, you don't need to update every time a new map CD or DVD is released. I'm not aware of any subscription services for map updates, but some devices are starting to incorporate traffic and weather information for your route, which will probably require a subscription.