With add-ons iPod can be played over a radio receiver:

Getting an iPod or other digital music player is great fun for the first few months that you own it. But after a while of carrying around a good chunk of your musical collection in your pocket, the novelty does wear off. That's when it's time to start buying accessories that can make it do more.

Two that have caught our attention in recent weeks do roughly the same thing. They use FM radio frequencies to let you play the music stored on an iPod over a nearby radio receiver. This solves the problem of playing music from the device on anything other than headphones without the need to buy an extra pair of speakers or negotiate a physical connection between the iPod and, say, a stereo setup.

....The iTrip is an attractive add-on for the iPod that plugs directly into the headphone port. Plug it in, and as long as you're within ten to 30 feet of an FM radio, you can play the music on your iPod over that radio.

....Belkin Components, another company with a huge catalog of curious peripherals you never thought you'd need until you actually see them, this week announced a similar iPod add-on called the TuneCast. It's being aimed at iPod owners but will work with any audio source with a compatible headphone jack--including PCs or laptops. [Forbes]