That doesn't hold water anymore.
The CEO and auditors want BlackBerrys and BES and iPhones and iPads.
You can do secure mobile device management and if you think your employees don't already have multiple devices, you are wrong.
Secure your ActiveSync environment. Discuss availability of secure VPN tunnels with your VPN environment. Write processes and proceudres around what is and is not allowed. Push down equivalent security policies to all devices.
It can (and must) be done right.