We have an alternative routing for Diamondcard that utilizes grey routes. These are routes that are much cheaper in pricing. Cheaper routes also give lower call quality as well as lower Average Call Duration (ACD) and lower Average Success Ratio (ASR). Lower ASR means it takes more attempts to get a call through. In some cases certain destinations may not work at all.
We have optimized our grey routing to maximize the possibility of calls going through. But even with this optimization, we will not process any call quality complaints for Grey Routes. If you want things cheap, this is how it is.