The major question in everyone’s mind has been whether Windows Phone 7 Series will support multi-tasking or not. We know that it will have push notifications built into the OS just like the iPhone, but now Mary Jo Foley has confirmation that just like the iPhone, it also wouldn’t allow third party apps to run in the background. Only Microsoft’s own applications will have that capability.
Mary Jo Foley found this from Kindel:
Kindel said Microsoft’s own “experiences” which are part of the Windows Phone 7 will allow for multitasking (i.e., music playing in the background while you’re doing e-mail). But third party applications won’t have the same multitasking capabilities, Kindel said.Developers will be able to use things like notifications to create the illusion that applications are always live. In addition, the Live tiles that are part of the new UI will be constantly updated in real time (also through notifications). Over time, as things like battery life, network utilization and application predictability improve for the Windows Phone platform, Microsoft will make more multitasking support available for all applications, Kindel said.
I did a little searching of my own in the UI design and interaction guide for Windows Phone 7 Series and found that the back button will also be used for application switching.
Whether this will be like the Alt-Tab is functionality is not yet none, but my best guess would be no. This would probably work like how the back button works in Android phones. Hopefully Microsoft would allow applications to run simultaneously as in Android as soon as possible instead of following the iPhone way as obvious from Kindel.