You will have to download a small app that does the test.
All of the result icons should be green.
This test found a failing modem for me. It was discarding 17% of the outbound packets. That made an unintelligible mess of the outbound audio.
Telo with 2 Handsets, a Linx, and a Safety Phone
Telo2 with 2 Handsets and a Linx