Martin,
Sorry for the time I took to answer your weustion, but I asked the provider and they ignored me
. But now surfing their own forum I found that some people running NCH's Axon have the same problem. To them solve, the need to enable an option called: Disable call activity polling (only use if call breaks after 60 seconds).
I don't know if it helps, but I also asked them again the information. I also exchanged some informations with other people in the voxalot forums and some other users using this provider have no complain about this issue, while other have.
Jean