If my car is Satellite radio ready, what additional equipment do I need?

I have a subscription to Sirius and a portable (suction cups) radio in my other vehicle. I bought a new car with built in navigation and is satellite ready. I want to add the satellite radio. What else do I need to purchase (besides the additional $6.95+/- a month for another subscription).to hook this up? |||If you are working with a factory radio, you need to contact a dealer to have the sat tuner installed.|||If you car is like my Toyota, with nav system and "satellite ready", you'll have to buy the radio add-on at your dealer and have them install it and the antenna (unless your car already has the antenna on the roof). It is ridiculously expensive at around $600. I prefer to go with the less expensive external portable solution, such as the one you already have.