I don't know if MCI "remembers" the phone number used to collect 25k, but I'm sure that they remember your FF number. I signed up for the MCI offer back in July, and a couple of months later I signed up for another phone line. (At a different address) I gave the same FF number both times. When I went to check the account for my second line some time later at www.mci.com/service , it also showed the miles I earned with my first phone line!