Google search suggests that FaceTime registration may use silent SMS messages. If your carrier doesn't support those, you might see legitimate REG-RESP (Registration Response) messages that otherwise wouldn't be shown.
The other possibility is that some scammer is sending these messages.
If these are FaceTime registration messages, or a scammer's attempt at forging them, it seems reasonable that the "n=" clause might refer to a phone number. "+39" is the international country code for Italy. The rest of the digits might be a phone number in Italy. Either yours (if the message is legitimate) - or a scammer's!
I think I will ask the Moderators to redact that part of your post, just in case …