I just had a local car audio dealer install an XM radio for my 2004 Prius. Toyota made the part but wouldn't install it because they couldn't verify it was for the Prius. Not only is it compatible and does it integrate perfectly into the JBL 6 disk changer, but there are even voice commands for it which were already in the NAV system. The touch screen buttons work perfectly too. This unit is available at CoastalEtech.com for much less than Toyota charges . Those people are very knowledgable and more helpful and friendly to their customers than you will ever see anywhere else. XM sounds great and the music selection is awesome. This web dealer also sells other high tech items for the Prius - check it out.

 

A lot of times the same companies that install car alarms or remote starter packages can also do custom radio installs. As melephant points out there's no reason to rely only on the dealer for this kind of install.