Since HTC announced the Shift there has been some confusion about how the two operating systems on the device play together. What can you do in each one? Do they talk?
Well I have to preface this whole section by stating that as far as I know the software on the unit I had to evaluate is not the final version that will be on the devices when they ship.
In Windows Mobile...
The WM6 installation on the Shift has been stripped down and customized. It is important to note that even though the device includes the 3G radio there is no phone application. The Shift is not a voice device. When you access the WM interface you are presented with a heavily customized Today screen.
This gives you access to your next couple of appointments, the date, time and calendar. There are also buttons to access your full calendar, email, SMS, contacts, weather information and some settings.
The weather interface is quite nice - cool thunder storms tomorrow :)
The settings button takes you into an explorer view that gives you access:
Notice there are a bunch of things that are usually in WM6 that are missing? Most of the settings interfaces have been replaced. Don't expect to add too many applications either. There is no programs folder so you would have to launch them through the file explorer. And there is not much memory for running applications either.
The HTC Debug Tools folder in the settings folder gives you a bunch of little utils. I don't know if this is going to be the same in the released version.
The bottom most icon in that - oops name was cut off - is called USBTool. This offers a menu with two options - cable in and cable out. When you select cable in with Vista running it creates a virtual USB connection between the two personalities of the HTC Shift. This allows you to run up Mobile Device Center and explore the WM OS from Vista. This makes it easier to set up things like Exchange ActiveSync.
The Windows Mobile OS stays running even when the Vista OS is sleeping or powered off. If you configure it to use Direct Push you can receive your Exchange email even when Vista is off. If you prefer or if you don't have an email account with Direct Push, you can use the virtual USB cable described above to sync directly with the local copy of Outlook in the Vista environment. Of course in this configuration you will only see in WM a copy of what is in Vista. You will not receive new emails while Vista is not running.
In Vista...
In Vista there is also a Connection Manager type of application that is called - for reasons that escape me - The Shag Control! This is a fairly clean interface that gives you access to connection management, power management and other settings. There is a gem buried in there - here's a tour:
Opinion
Given how stripped down the WM OS is I almost wondered why they bothered doing it that way. I'm not saying that it is not useful - far from it - but I would almost rather that the second OS was implemented as a sideshow host rather than a WM environment. You would not be able to do the push email, but you could access the data from the local instance of Outlook... and potentially do a bunch of other cool things. Food for thought.