There are two kinds of media commonly used for communication: electromagnetic (EM) radiation and etheric.
In AIF, electromagnetic communication has existed longer than most civilizations, and has variations of dizzying complexity. It includes everything from walkie-talkies to microwave lasers. EM communication is generally restricted to short-range use, because of the inherent limitation of the waves propagating at the speed of light means that there is signficant lag if the distances between transmitter and receiver is too great.
There are several advantages for using EM communications, however. First there are it's ubiquitous use, and the simplicity of the requisite hardware. Secondly, "tight beam" variants are very stealthy because limited diffused radiation. Frequencies useful for broad communication can be jammed with emitters capable of the same wavelength. Meanwhile, the "line of sight" nature of "tight beam" communication cannot be jammed without inserting interstitial media that can block the radiation.
The primary advantage of etheric communication is it's instantaneous-ness. For craft capable of travelling superluminally, it is absolutely essential to have etheric communication systems on board in order to have any contact with the rest of the universe while travelling. A superluminal craft that becomes stranded or adrift in deep space without etheric communication is in deep trouble indeed. The range of etheric communication is the larger of the receiver and transmitter - thus a 1km-range pin can communicate across interstellar space, when in contact with another etheric communication system of sufficient range.
The primary disadvantage of etheric communication is extremely public nature of the media. While the content can be encoded to delay others from understanding it (until they get a mathematician to decode it), it still states quite clearly that there is SOMEONE as the source of the transmission. Moreover, with sophisticated sensor equipment (or one of those mathematicians again) it is usually possible to locate the transmitter.
Etheric communication can be jammed by another etheric system of equal or greater power (the power generally being the range). This applies to both transmitting and receiving. Note that if the jamming device is in range of both the transmitter and the receiver, both must be more powerful than the jammer in order to be able to neglect it. Etheric communication systems or sensor systems can be used for jamming.
The "holy grail" of secure communication is alternate ether communication. This is where the receiver and transmitter manipulate the ether of another universe for communication - meaning that it's undetectable and unable to be jammed by anyone else. This is purely theoretical, and exists in the realm of AIF-fantasy beside 2-variable fold-space generators and the legends of the Arbiters and BRG.
A Note on Jamming
For simplicity sake (no, really) we usually say that all jamming is effective in a sphere whose radius is the range of the jamming device. We also generally say that the origin of the jamming is not obvious from inside the effected volume, because of insufficient clarity. Likewise, the location of the jamming device is easily determined from outside the jammed volume by extrapolation to the center of the sphere of influence. Yeah, we know this is kind of silly when applying to the electromagnetic, but we're lazy.