I found this app the other day called Seamless, and I have to say, it’s definitely well worth the 99 cents. Basically, if you have the same song or playlist synced to your mobile device and your computer you can switch listening from one to the other – seamlessly.
This is perfect for me because I make playlists for each month and listen to them on all of my devices. But sometimes I’ll be in my room using iTunes on my laptop but will need to do laundry in another room. The playlist is on my iPhone, but unless you’re willing to wait until the end of a song there’s always an interruption. Tap a button on the app, and it fades out from the laptop to the iPhone. There’s no lag, and no interruption.
The app is available from the iTunes Store for your iPhone/iPad/iPod Touch, but keep in mind you’ll need to download it’s sister app (but this one is free) from the Mac App Store.