Uninformed data point - our organization elected to go with Treos for those staff with company phones. People are thrilled with the functionality. Having been a Palm/Outlook user for several years, I would personally welcome the opportunity to carry only one device instead of two.
HOWEVER, more than one of my colleagues reports that the Treo phone reception quality is sometimes suboptimal.
The speculation here is that Blackberry will ultimately be odd-platform-out in the phone/PDA convergence wars. Probably Seattle bias
