Now you have to avoid the mathematician's mistake of numbering everything. Do you really keep track of spoken conversations you have, by a number assigned when you start them? Of course not. Often just the person is enough to identify it, sometimes it is person plus a subject. Sometimes something else. Heck, a random icon, for subject might be more useful than a number. (wordpress, for instance, assigns a geometric icon to any identified but not registered user).
no subject
Now you have to avoid the mathematician's mistake of numbering everything. Do you really keep track of spoken conversations you have, by a number assigned when you start them? Of course not. Often just the person is enough to identify it, sometimes it is person plus a subject. Sometimes something else. Heck, a random icon, for subject might be more useful than a number. (wordpress, for instance, assigns a geometric icon to any identified but not registered user).