Over the years, we've encountered instances where call quality may seemed to have swayed, while all our systems and the Operator network have been functioning with the utmost efficiency.

Besides that, the issues seem to get resolved by itself after certain duration and yet, without any intervention from our end.

On that note, we organized a survey to determine the things that agents / customers can do to maintain call quality at their end and found that the following parameters may have an impact on the call quality -

Voice calls prefer 2G over 3G or 4G

This can be achieved by switching the mobile data off on your handset, before a call

More than half of the members who participated in the survey confirmed this outcome after testing this for over a week's time.

Generally, you can say, for GSM -
-105 to -100 = Bad/drop call
-99 to -90 = Getting bad/signal may break up
-89 to -80 = OK/shouldn't have problems, but maybe
-79 to -65 = Good
Over -65 = Excellent

You may find more relevant information here.

Sending or receiving SMS in the middle of a call

While having to receive an SMS is not something that can be controlled, it should be considered while experiencing a poor call quality or discrepancy while in between a call as well.

Since mobile data and SMSs use part of the bandwidth / spectrum that gets allocated for a call, controlling their usage can indeed be of great help with improving the call quality and also the overall experience of a call.