According to Microsoft Technical Evangelist Yochay Kiriaty, "Windows Phone allows only one application to run at any given time in the foreground, and no 3rd party applications are allowed to run in the background", he said in a note to developers Tuesday, while talking about tombstoning, a "procedure in which the operating system terminates an application’s process when the user navigates away from the application. The operating system maintains state information about the application. If the user navigates back to the application, the operating system restarts the application process and passes the state data back to the application".
It looks like when a user will navigate away from the application to "either to a chooser like picture chooser, or to a launcher like phone call, Windows Phone operating system terminates your application". Nevertheless, some Microsoft processes will be able to run resident in the memory.
How many third party applications do you currently run on your Windows Phone regularly at any given moment? How do you switch between them? Do you have a need for an "always running" third party 24/7? Tell us your thoughts!