Hi,
This is not a Cisco issue but is a wholesale telecom issue. I assume you were calling to the middle east, Germany, Turkey or South Africa? Below is a response I recently posted to a Google thread explaining the issue.
This is a known issue primarily to the middle east but to other countries as well. I work for a telecom carrier and about two years ago we started seeing this issue to Saudi Arabia and the UAE. We have also see it to Turkey, Germany and lastly South Africa. Basically what is happening is there is a carrier in route that is messing with the call. The way telecom works is every carrier pays he next carrier per minute for the call. So for instance if you are using Google Voice they may send the call to British Telecom. British Telecom may then hand of the call to Verizon. Verizon may then have relationship with DU (a carrier in Saudi Arabia) which completes the call to the mobile headset.
In telecom it's all about how much you pay per minute for the call and how much you can then sell it for. Let's change the above scenario but instead of Verizon sending the call to DU (which is direct in Saudi Arabia) they have a carrier that is a fraction cheaper. So instead of paying 0.14 per minute (the going wholesale rate to Saudi Arabia)) this carrier only charges them 0.13. They are going to prefer using the carrier that cost 0.13 to save 0.01 per minute. Now this may not sound like a lot but go and multiply that by 10 million minutes a month (aka $100,000) it adds up. So why is this shady carrier messing with your audio? What they do is they take the call from Verizon. Now when most people start a call they start with "hello". So let's say your calling your mom in Germany. She picks up and says "hello", you say back "hi how are you". She then says "I am fine". They will record the first few seconds of the call "Hello, I am fine"". Now say you speak for 30 seconds straight, telling your mom how school was, how the dog is etc. You then both talk for a bit. What happens next is this shady carrier will hang up on your mom. They will play back to you the beginning of the call where your mom says "Hello, I am fine". If you never experienced this issue before you will think your mom did not hear your 30 second talk on how school is how the dog is behaving etc. So you repeat everything you just said. This "carrier" is now making 0.13 on a call that is going no where. So they are charging Verizon for those 30 seconds even though they are no longer paying for it as they already told the carrier in Germany to hang up the call.
Another key part in telecom is being able to re-produce an issue. Whenever you open a ticket with a provider they will try to re-produce the issue. The people doing this fraud know this and set up their systems to not do this to every call. They only do it every so often so it makes it impossible to track the issue. We have this issue with all major carriers such as British Telecom, Verizon, TI Sparkle, BICS (aka BelgaCom) etc. The only way to root out the issue is to complain to your provider and insist that they complain to their upstream providers.
TBH in the beginning I thought like others have that perhaps it was a buffer issue on an old T1/E1 circuit but then we noticed that the issue as spreading. First it was just to two middle eastern countries and then it spread to countries that were the wholesale telecom rates were not stable. For instance South Africa was a stable route for many years. recently they changed the rates for calls that came in from out of the country by 600% (where the wholesale rate was 0.02 per minute it went to 0.12 per minute). As always the large carriers will try to buy at the lowest rate and sell at the highest. This introduces the same seedy carriers and their little games to earn a small profit at your expense.
