I have always and will always believe that communication is handled through subspace. A transmission is sent from one ship, hits a comm array and gets redirected either to another comm array, a jump node, or the recipient ship.
Because subspace is needed for communication, when you disable a ship's comm system it is disabled. Mobile phones and other hand-held devices are useless since they don't have any subspace capability (unless it gets zapped by Doctor Who or something).
Communication with Sol probably has taken place but the GTVA don't want us to know about it. (conspiracy)