As per Joe Belfiore, Windows Phone 7 will soon support multitasking. This Multi-tasking support will be coming to Windows Phone 7 sometime later this year.
Key features of WP7 MultiTasking
* App Switching would be faster
* Task Switcher will let you switch between the apps. It would be accessible by pressing and holding back button.
* Third Party support for Music Apps. You can play the music in background while doing other tasks. The video shows Belfiore playing a song from Slacker Music app. He switched to check his mails and still the music was playing.
It would be normal free update of Windows Phone 7.
Here’s a video explaining the support that would be added in WP7 in late 2011.