I was responding to trekkiebaggio's
comment about why Carter's and Fusco's numbers didn't come up along with Reese's (I assume he meant at the same time).
Dramatically, it makes sense for the call at the end to be about the Machine warning Finch about Carter (sort of a way of expressing regret --like if he had just picked up the phone in time...), but I tend to lean toward the camp that says it was the Machine keeping Harold away from the shooting of Reese and Carter to keep him safe. The Machine sees things in real time, so it would have known Carter had already been shot and stopped calling at that point. I think at first it might have been keeping Harold away to keep him out of the line of fire, but after that it kept ringing to spare him the sight of Carter dying up close and personal, since he may not be able to handle it. It does seem to care about Finch and his emotional state a great deal, going so far as to assist in his love life.