It's a nice idea, and I'm sure equivalents exist on other mobile platforms - Karaoke One includes instrumental tracks for popular music and guides you through the lyrics on your Windows Phone while you warble along. The catch? Well, you'll need to pay for most of the streamed tracks you choose to sing to, though various passes and genre bundles are available. 

From the Store description:

Karaoke One offers you the best Karaoke experience on all platforms and devices, with thousands songs coming soon. 
Great MP3 and WAV studio recorded backing tracks, synced lyrics, awesome design, constant updates...and much more!

Here's Karaoke One in action:

A smattering of free backing tracks (one in each playlist) let you play with the idea and practice your singing... The lyrics colour in red as they're (supposed to be) sung, so it's easy to keep in step.

You buy individual commercial tracks or entire playlists, or indeed the 'Full Time Pass', but stocking up karaoke material for your party could work out expensive. Also note that, as per the left screenshot, a lot of content simply isn't in place yet...

The app's ambitions are high, including iOS and Android, both of which are 'coming soon' too. Clearly very early days, though at least the developer started with a Windows Phone version!

Another of the suggested genres, this time letting you croon some classically-crafted and deap and meaningful Richie lyrics....

It's early days for Karaoke One - all the content that's not there yet, the lack of a search function, and so on. You can grab it in the Store now if you think you might have fun with this.