Originally Posted by 9Dave
So you know - the XM add-on is by a complete external radio. Check the Garmin site to make sure you are looking for one that is compatible with your 550.
Actually you just need an GXM-30 antenna that plugs into the zumo 550 cradle then follow the prompts on the screen to activate service. With service, you get XM radio, traffic alerts and weather updates/forecasts.