Andreas Hammar has done a little experiment on the Tango emulator to prove that Windows Phone Tango on 256 MB devices does in fact have Fast App Switching, not just Tombstoning. This will however only work if apps do not use much memory, as larger apps will invariable invoke tomb stoning.
In fact the documentation which first confirmed that Fast App Switching would not work on 256 MB devices have been updated on MSDN and now reads:
Fast Application Switching is supported on 256-MB devices. However, because keeping applications in a dormant state for Fast Application Switching is dependent on the phoneâ€™s available memory, an application running on 256-MB devices will be terminated and tombstoned more often and more quickly than the same application running on a phone with more memory
While the news does not significantly change the user experience on Tango devices, it is at least reassuring to know Tango handsets are not running some hacked version of Windows Phone, and still have most of the subsystems still present.
Read much more detail at JayWay.com here.