imessage going through as an email
I have just got my new iphone 4 today and when I try to send a message to my friend who also has an iphone she says although sent as an imessage it comes through as an email. When I go to receive at in settings it has my mobile no which is greyed out and it has my email address in bold so she suggested deleting my email from this but the option to delete is greyed out. Has anyone got any ideas what to do?
iPhone 4, iOS 5.1.1