I get a message (dont know who from) with the Subject: Registration. The body of the message says: Your handheld has been registered with the wireless network.

Any clues?

It is a standard message that arrives at your device when you are fully registered on the network. As this is your 2nd post, I would assume you are new to Blackberry and just got your device.

Pretty self explanatory. Not a difficult inference to make that this is from the network confirming your registration.

Welcome to blackberry.