Yes. Each call should be using only 100 Kbps max, so you have more than enough bandwidth. We had call quality issues initially as well, and it turned out the QoS had not been configured correctly on the router.
Sustainable Printing Goes
Far Beyond Using FSC Certified
or Recycled Paper
This informative paper on deinking: demand, principles, problems and solutions also explains why printing technologies are not all equally compatible with paper recycling systems; and why just a small fraction of printed material in the paper can cause difficulties. Link To White Paper