it used to be by default bt facebook stopped that a while ago. lt used to be whichever email you register facebook account with was the one they were going to sent all alerts and messages.
But they have since stopped it since they have now there own email service eg firstname.lastname@example.org. They ar trying to retain all the revenues, bt l have not registered and use the email to test if they are sending alerts there.
Should it be the case, settings can be the same imap settings on most 3g phones