It is simple
The Battlestars are basic. They just use what works. They don't network the computers so the Cylons cannot insert viruses into the system.
At least the Galactica doesn't.
Notice how they also have those crazy howler phones you see in WW2 warships?
Since we are on the subject, keep in mind, there are 8 different Cylon humanoid models, and we have only seen four of them.
There are any number of major characters that could be Cylon agents..
Like Sol Tighe's wife, or Admiral Cain.
Landfall of the eye has now taken place per Fox.
The reporter who did the story on Galactica is a Cylon. Of course, so is Dan Rather.