Determining the reason for poor call quality should be a troubleshooting exercise any good telecommunications partner should be able to get to the bottom of.
The quality of the phone system is dictated by a lot of factors. It is not usually the fault of the SIP Trunk provider, though it’s always possible!
Using a Softphone
Quality of Headset
Ensure your internet connection has enough bandwidth to support your call. You don’t need much speed to support VoIP, but if someone is saturating the bandwidth in a video conference, or downloading or watching a video online, you will run into quality issues.
A common practice is to implement QoS or Packet Prioritization.
This will make sure that VoIP traffic gets priority over all other traffic on the network ensuring that there is enough bandwidth for the VoIP call. If you are having issues with bandwidth, check which codec you are currently using and possibly change to one which requires less bandwidth. Find out a bit more about codecs here.
Quality of the other persons line
Aged networking hardware
If switches or hubs are being daisy chained, this may be creating a bottleneck for network traffic and it’s possible your call will not have enough local bandwidth to reliability deliver good voice quality.