Ring signal frequency selection
Here supports four types of ring signal frequency, 20Hz, 25Hz, 30Hz & 50Hz.
User can choose a proper ring signal frequency according to the ring frequency of
the phone user adopts.
Usually the ring signal frequency adopted in the U.S.A. is 20Hz.
The ring signal frequency in Europe is 25Hz.
The ring signal frequency adopted by the major countries in the world ranges from
