in case you have not read the wiki page, these numbers are sub tones that are used to , along with fre frequency that is transmitted, to access other radios or repeaters. Sort of wedding out signals. Some departments go to CTCSS, so they transmit the tones, and they have to have the tone in to receive a signal. The radio specturm is only so big so agencies or private individuals use these tones to weed out signals they don't want to hear. Besides the sub tones, there are dcs codes, that allow the receivers to clean up the radio receivers . Now when someone is on the air on a specific frequency with a tone, most radios have a feature that they can not transmit until the other signal has ceased.