They send you a message, BES replies back. This is only during an activation. It's not a simple automated response. After the ETP.DAT file hits exchange and BES grabs it, it replies back. Here's a sample:
Code:
This message is used to carry data between the BlackBerry Handheld and an associated server. Please do not delete, move or respond to this message - it will be processed by the server.
BEGINETP 10
Awx0jPsAAAAAAQ!!
ENDETP 1660784311
It also has an ETP.DAT file.
I'm guessing it's a simple response saying, yup - that person belongs to me.