Sac
I bet they spent today trying to figure out why he picked the certain number hoping it might lead them to him. They probably found nothing and put the phone number into action for the sniper to use at his request. I bet he calls it and I bet he makes his calls brief so that they cannot be traced. All he needs is a few seconds to make a statement to someone. He no longer has to leave tarot cards or notes that might blow away at each scene. Something tells me he has been leaving notes for them at each scene, but they have been missed or blew away and were lost. The sniper is not totally stupid... he wants to talk to someone specifically, maybe Moose, shucks he may even want to talk to the president directly.
This theory assumes he left a message requesting a specific phone no. be set up.