The voice inter-communications devices used on the "Galactica" are actually the TA-1/PT field telephone, as used by the military for decades.
Opening credits say there are 47,858 human survivors.
When Commander Adama is listening to the pilots during their asteroid weapons training his "Listening Device" is actually an AM-7162 which is the Master Control Station for the AN/VIC-2, mechanized military vehicle intercom system. It also has a modified LS-685 loud speaker connected to it where Receiver/Transmitter #1 should connect which would also power this device. He turns the center knob to increase the volume; this is actually the switch to turn on the "Internal Accent" which activates a noise filter.