According to RIM, the device key is used to encrypt all messages. The device tells the corporate server its key and the corporate server encrypts every message

According to RIM, the device key is used to encrypt all messages. The device tells the corporate server its key and the corporate server encrypts every message before it is sent. There is no common key between the telco and handset for the message content. (This is on top of the VPN link etc.) Of course it's hard to verify RIM's claims since the whole system is run by them.