ClearCom,
Telex RTS, and
Telex AudioCom are three popular flavors of wired "party
line"
intercom systems. They use one or more
base stations and then beltpacks, with optional wireless beltpacks. You can also add
speaker stations, tie into paging systems,
etc.
The various stations are interconnected using standard
XLR microphone cable, and allow users to push-to-talk or leave the talk latched and talk freely. Either way, multiple users can talk at once, which is a huge plus over two-way radio systems (there are options that can be set to, for example, allow the
stage manager to override the talk buttons on all remote stations if needed).
They're definitely more expensive, but well worth it.
ClearCom is the most common in the
theatre world, although of the three I've noted, it's not necessarily the best. It's unbalanced, so very susceptible to hum from all sorts of things.
Telex AudioCom is great because it uses a balanced audio signal, so you don't get much interference/hum. The tradeoff is that it uses a theoretically super-audible tone for the
call light signal instead of ClearCom's method of shorting out two of the pins, and you can hear it whine softly in the
headset when it's pressed. It's also very rare; I've only once seen it at a
venue (an
arena I played last week, actually).
Telex RTS is very common in TV production, and in some theatres and arenas. It's huge benefit is that it fits two channels down one three-pin
XLR cable, where the other methods use one cable per
channel. The downside of this is that it by nature needs to use an unbalanced signal, so is not only susceptible to the same hum that ClearCom is, but can get lots of crosstalk from having two channels in the same cable (depending on other factors involved in cabling far too complex to get into here, of course).
If you want to stick with two-way radios, get good headsets that you/your crew like (everybody has their own preferenecs) to go with appropriate Motorola Radius two-way radios or similar. Don't use FRS family radios, as many do, because it is illegal to use them for commercial use.
That help a
bit?