Ok... I get it. We used Hollywood call-signs in training when CEOIs weren't available. When they were, it was back to alpha-numerics, and callsigns and freqs were changed every 24 hours... When we went to digital commo back in the late 90s, we were able to go back to the Hollywood callsigns, and the numbers changed every day, but the prefix remained the same. The FO's, for instance, would talk to our FDC as, "Shooter two-five, this is Thunder one one" kinda stuff... Everyone with a callsign in the SOI (new name for CEOI) had the same number that day that reflect who they were, but the prefix was battery-specific, like Alpha Battery was "Shooter", Bravo, "Cold Steel", and Charlie was, "Boomer", so on and so forth... The BMO from the arty could call the infantry BMO, and it would sound sometthing like, "Banger two two, this is Boomer two two, over", "two-two" being the number for all the BMOs in the brigade that day.
Clear as mud, right?