Third-party Windows Phone developer appeared to have beaten Microsoft, as they've figured out how to implement 3rd party application multitasking on Windows Phone without the help of Microsoft.
"Developer "JaxBot" has shown off his implementation of multitasking, which appears to work pretty well. The hack works when the user "half-presses" the camera button -- it opens and allows the user to select an app that's running -- then quickly switches to that app. It appears that they do run in the background, as JaxBot shows in his video a timer app that continues to count, even when away from the app. This hack could be a trick similar to the one that was recently shown off, where modifying a registry value allows for applications to continue running in the background, under a locked screen (which also, funnily enough, was developed by JaxBot)."
This solution allow full multitasking. Threads can run in the background, and perform tasks on the phone (display a message, navigate to a page, etc) while in the background. The reason why the timer jumps from 50 to 80 is because the text block that displays the current time stamp (read from the thread) is updated by a timer that ticks every second the application is in focus. It's technical mumbo-jumbo, but something I'd like to clarify: tasks can indeed run in the background.
[Via: Windows Phone Hacker]