I assume there are checks made (and delays (though we don't seem to see any on TNG)) when a crewman is on a planet or starbase.

   Most people have accepted that if a person is on a ship or starbase or someplace where the computers can monitor one's speech, the person doesn't have to tap his / her badge. If the person is exploring a planet or otherwise away from direct contact with the computer system, a tap on the comm badge will signify that the user wants to open a channel, and the person may or may not mention who he / she wishes to speak to (the must be some default, such as "the bridge of the last ship I left").

   "The speed of propagation of a subspace signal continues to be the limiting factor in any long-range communications. Subspace radio signals, even those tightly focused and radially polarized, will decay over time, as the energies forced across the subspace threshold will tend to 'surface' to become normal slower EM. As this decay occurs, enormous amounts of information are lost, since the modulated signal does not decay evenly. The propagation speed under ideal galactic conditions is equivalent to Warp Factor 9.9997. This places subspace radio about sixty times faster than the fastest starship, either existing or predicted. The phenomenon, which occurs at distances proportional to the peak radiated power of the outgoing beam with an upper distance limit of 22.65 light years, has necessitated the placement of untended relay booster beacons and small numbers of crew-tended communications bases at intervals of twenty light years, forming irregular strings of cells along major trade lanes and areas of ongoing exploration." -- TNG Tech Manual pg 99