[Olefin]

There could still be transatlantic cables still operational - i.e. communicating via telegraph or telephone and then using short wave radio to pass on the messages

Or they could be using repeater stations - i.e. ships spaced at intervals specifically for communications - especially if they are using low power communication mediums

Finally I could see the US could saving a couple of operational communications satellites as well and using them similiar to the one in Twilight 2013 that was put up for the Presidents "your on your own" speech- i.e. on a low orbit specifically used for very important orders - like the Omega evacuation - they can only stay up a few weeks at a time because they cant get them up to higher orbits with what few launch facilities and rockets they have left and are used sparingly since they have so few left - but during the time they are up they can use the full capacity of their comms equipment as to interacting via satellite -

for Omega it could have been used to transmit the order, get any USN ships still in European waters to meet at Bremerhaven with the Hancock and also to order the rendezvous that is mentioned in A River Runs Thru It - i.e. the ships that came out of Norfolk to escort them the last 1/3 of the way in - in a low orbit that only allowed the satellite to stay up a couple of months - long enough for beginning to end of Omega