How to resolve FXO disconnect/busy tone detection problem?!

Today I am going to show you how to get rid of above issue with FXO ports on Cisco routers.
The problem arises when you get connected to PSTN line, after the PSTN phone goes on-hook you hear a busy tone on your phone. 
  Of course, you can use standard cptones, but what to do if those will not work? 
We need to detect what is the frequency and cadence of the busy tones which come from PSTN line.
To begin with we need to install an audio program which is capable to analyze audio files(I am using Cool Edit pro for this purpose).
  Next what we are going to do is record those busy tones which come from PSTN. But it is not always possible to record over standard microphones. The best way to record busy tones is -

1. Call IP phone from PSTN. 
2. Go off-hook with IP phone. 
3. After call gets connected go on-hook with IP phone. 
4. You will hear a busy tone on PSTN phone which you should record via a quality microphone( I have used an Iphone of my friend) 
5. Download the audio file to your computer where you also installed audio program(e.g. Cool Edit pro.)
6. Open audio file with Cool Edit pro. You should see something like this: 

      7. Zoom in and select part of the audio as below.

       8. The cadence will be the length of the marked part of file(red marked on above pic.)
       9. Then Navigate to bottom panel and choose Analyze --> Show Frequency Analyze

     10. Put your cursor to the bottom part of line and note the frequency. In my case 460 Hz.

So we have cadence = 360 and frequency = 460. Go to configuration mode of your router and put following lines:

voice class custom-cptone busytone
 dualtone busy
  frequency 460 460
  cadence 360 360

Then just put voice class busytone under your voice port. Make necessary test call and be sure that FXO ports go on-hook when the PSTN phone hangs-up.

Thanks,
Nuran Afrasiyabov (CCIEV#29273)