Core is not so core for 2007

Microsoft created a shell-like Windows installation for Server 2008, called Server Core, which installs a minimum of interface components to the server, and allows for more processing power to be dedicated to the application systems.  While this would sound perfect for Exchange Server 2007, there are a few key things that will prohibit you from taking advantage of the Server Core system for your messaging servers.

First and foremost, since Exchange relies on things like PowerShell and .NET, you can't install Exchange on Server Core just yet.  Core doesn't support the installation of .NET or PowerShell (which relies on .NET), so even if you managed to get the installer to run; you'd fail all the pre-flight Exchange tests.

Also, Exchange Server is not impossible to administer without a GUI, but it is difficult to do so.  The majority of users would prefer to use a GUI to do most of the non-day-to-day stuff, and that's simply not an option where no GUI exists.  Server Core is literally a shell environment, the only thing you see on your desktop is a command line interface.

Microsoft doesn't have a clear statement on direction for running Exchange 2007 on Server Core in the future that I can find, so there is a good chance that this just won't become a supported solution.  It would have been great, since the reduced overhead of no GUI on the OS means more resources for the Exchange system itself, and since Exchange 2007 is designed to be run through PowerShell as a sole method of admin if necessary, Server Core would have been a great fit.

You can install Hyper-V to a Server Core platform (or just install the stand-alone version of Hyper-V server to the bare hardware), which would allow you to run Exchange Server 2007 in a VM.  However, with limited support for Exchange virtualization, and the fact that you'd be installing a full OS in the guest anyway, this probably won't be a helpful configuration.

My guess is that as Server Core continues to gain traction in the enterprise space, Microsoft will begin to find ways to get .NET into the platform.  It may never support the full Exchange 2007 system, but I suspect Server Core might eventually become the platform of choice for things like Hub/Transport, CAS, and Edge Services.