So... there's an FTL communications array that predates the war? I suppose it was pointless to hold on to the hope that this whole thing hadn't been retconned, but it's still pretty annoying. It does a lot to undermine the colonies' isolation that fed into the insurgency and was one of the reasons ONI was able to downplay the threat of the Covenant to the Earth's public. A direct, instant line from Earth to the colonies would've probably solved a lot of problems before they even cropped up.

Not to mention a lot of important events don't really make sense if they could've just picked up a phone and called Earth or Reach at any time. Like when they had to physically send a ship to find out what happened at Harvest. Or, you know, how in Contact Harvest it's explicitly mentioned that ships were the only means of sending messages between colonies.