I just learned the following on coverage of Operation Vigilant Resolve:

Because of the danger and the nature of the operation (the closing off of the roads, etc.)

Coverage has been assigned to a small embedded "pool" of reporters.

(When a "pool system" is in effect, those selected reporters agree to share their raw data/notes/reporting with everyone else.)

MSNBC played a phone message from one (so in effect they admit that they do not have anyone on the scene):