Resistance communication

The Resistance communicates through several means and devices.

Communications radio
In the Underground Railroad or Resistance outposts, they need some type of communications to keep in touch with other bases. A Communications Radio was just a plain old radio that is now used to call for reinforcements, talk about whats going on, or just hanging out. Communication Radios are usually never bothered if a Rebel base is under attack.

Communications station
Sometimes in specal bases, Communication Radios aren't enough. Communications Stations usually come with a monitor, a Communications Radio, and some other technology seen. Communications Stations can sometimes be interupted. Like in Half-Life 2: Episode Two when Alyx Vance was talking to her dad, Isaac Kleiner, and Arne Magnusson, a Hunter-Chopper appears and interupts the transmission. Also on the way to the safe zone, Alyx and Gordon Freeman were contacting the base, but was interupted by a Combine Advisor (that was possibly to be inside the barn up ahead).

Portable communications station
Only one can be seen and its at the beginning of Episode One where Alyx tries to contact her Dad with the Help of Dog. It seems like it is portable since Alyx mentions when Gordon and her are on the move to the Citadel that she asks Dog to pack up the screen is also black and white.