I notice on my Evo Shift, when I link two or more contacts in the People application, the phone numbers for all such contacts appear on each contact's page. That is, if I have, say, 2 phone numbers for each of 2 contacts, and then I link those 2 contacts, then each of those 2 contacts will have 4 phone numbers now (the 4 phone numbers of those 2 contacts). Why would this be useful at all?
