CellCom is actually DECT technology (Cellphones residential kissing cousin). For each antenna on the system, you can link up 5 beltpacks - the standard cellcom system comes with 2 antennas - with the splitter box, you can get 8 (or 10, I cannot remember) antennas onto the system. It's a very good system, beautifully clear, and was first designed to integrate into the Clearcom matrix system, so that you could have a remote matrix station, instead of being limited to party line talking. The audio quality is beautiful - and in a corporate environment, they cannot be beaten (imagine, client headset only has access to talk to the technical director and cannot hear any other conversation, camera guys talk directly to the vision switcher, spots to the lighting director.... you can reduce what you hear in your headset to exactly what you need, and no more)
For those without the big budgets, HME make a nice little intercom - it only has 2 limitations 1) you can only have 4 beltpacks talking at once, per base station and 2) it does not use standard headset connectors. It is perfect for theatre though, and I have seen the beltpacks (which are tiny) thrown (with force) down two flights of stairs and survive... the headsets are a weak point though.
RTS and Clearcom both make an analogue wireless system. They are a better quality audio than the HME system... not as cheap though, and they are in the UHF spectrum and can interefere with radio mics. The RTS solution is also (from memory) 1 beltpack per master station, whilst Clearcoms WBS system is 4.
The benefit to all of the above systems is they can plug straight into your existing two wire systems (ClearCom, RTS, TechPro,
)
Just some links (now that I have time):
RTS, marketed as Telex RadioCom
hereClearcom Cellcom/Freespeak DECT system
hereClearcom WBS UHF Wireless Coms
hereHME's 4 channel 'cheap' solution
hereClearcom also make the Tempest range... never used them, but they opperate on 2.4GHz, which is a crowded area of the spectrum
here