"Back in 2006 we produced a Total Cost of Ownership (TCO) Whitepaper focusing on the total cost of ownership of a Mobile Messaging solution using RIM Blackberry or Exchange and Windows Mobile. We have just published a new version of that study which now includes data from over 160 Enterprise customers. Those customers used either Blackberry or Windows Mobile and we have included their real world TCO metrics in this study."
As you might guess, WM comes out ahead in this study. I'm not surprised by this. It is a superior platform in my opinion. The study shows WM has a 20-28% TCO advantage. For more details head over to Jason Langidge's WebLog and give it a read.