I texted an old friend of mine and I know they do not have my new number but they automically knew it was me because my name shows up in their phone.
How do they know this?
My logic is that facebook sets your name attached to your phone number or is it associated with the email addresses on the iphone?
Another possible is if you both have iPhones then the message was probably sent via imessage. That system uses your apple ID for identification (at least that is my understanding) and I assume that would have not been changed when you changed phone numbers.
Facebook it must have to do with. I have all my friends info from facebook like birthdays etc that i didnt punch into in my contacts. There's a setting or it asks you if you want your friends info. if you left your number in your profile the friends can have it in there contacts I think also birthday address etc.