The scope of a patent is defined by the claims. By the same token, what is infringed and what is invalidating prior art is also defined by the claims. So to invalidate a patent you need to find prior art based on the claims.
Claim 1 of US6463131 is as follows:
- A system for notifying a user of an incoming communication event, comprising:
means for determining a characteristic of the communication event;
means for selecting a notification based on the characteristic;
means for sending the user the selected notification;
means for receiving a selection from the user indicating a format for
delivery of further information regarding the communication event; and
means for allowing the further information regarding the communication
event to be sent to the user in the selected format.
There's an equally broad method claim, but it is not substantially different in terms of scope, so this can suffice.
At a high level, this claim is about the rather narrow aspects of notifications that deals with selecting a notification method based on some "characteristic" of a "communication event", and allowing the user to select a format in which to receive "further information" about the event. The meanings of the words in quotes would be defined by the specification, if they have no common meaning as such.
So if you want to find prior art that invalidates this claim, you'd need to find one or more (usually up to three) prior art references that, taken together, describe each and every element of the claim. I haven't read the three references you cited, but do any of them, either by themselves or in combination, cover all the elements of this claim?