I was briefing to fly my 2nd sortie of Phase 3 down at Corpus. Went into the briefing room, everything was normal. Came out of the briefing room, everyone was packed around the little TV in the break room. We couldn't let a little thing like some idiot running into a building on a clear blue day stop the UPT syllabus, so we stepped. Ready to go, no ATIS, no response from tower, then we hear a message over the ATIS freq and on Guard shortly thereafter: "All NAS Corpus Christi aircraft are directed to discontinue training and return to base immediately, one to a full stop only. Repeat..." As I lowered the crew stairs, one of the MX dudes was jogging over screaming something about the Pentagon getting hit. The rest of the morning was spent in front of that little break room TV in a sort of daze. Pilot training suddenly had a whole new meaning.