By default, the bases selector is tuned to your starting base, you can contact it by using presets. The A/G button is used for VHF frequency, C/F for UHF. All the presets are in the kneeboard.
Your flight's frequency is on the preset channel 1 (top row buttons). H button is for transmitting/receiving on guard frequency. There's also a possibility to monitor both selected and guard frequency, but this feature does not work (devs, hint :)).
Other "special channels" in the same row, labeled 2 and no label can be set in mission editor. Button "-" is used for manual tuning.
Other flights channels are located in the bottom row (buttons 1-9), used with the left knob (group selector). The presets are automaticaly generated and can be found in the kneepad.
It does work. :)
You either have easy comms turned on, or you messed with the radio selector knob, which will fry the radio (bug). :D