There has been some buzz recently about further changes to the Windows Mobile 6.5 user experience since it was announced and the developer emulators released. For example this article has some screenshots:-
It shows changes to the soft-key menus at the bottom of the screen and a complete revamp of the tab control. Further on in this article there is a description of some registry keys which can be used to enable recording of voice calls which enables a new menu item inside the phone application. As it turns out these registry keys work on Windows Mobile 6.1 also as I was able to test on an HTC Touch Diamond 2. For reference the registry settings are:-
Soft reset the device after setting these and you should notice a new Record menu item when in a phone call. You can listen to the recordings using the Notes application, they are given a unique filename with the timestamp of the call.