It works... Turn radio on and then use rotary wheel to switch to the airports number (1, 2, 3, etc).
An example:
Gudauta has frequencies 130,00MHz, 40,20MHz and 259.00 MHz. In the mission editor select your Sabre and then the 'antenna' tab (far right). There you can see which frequencies are set to which number on the rotary wheel. So in order to contact Gudauta ATC the 259.00 MHz needs to be in the list.