another problem with G/S HT 386: no sound when calling *031 numbers
 

I have a C450IP at home, and a G/S HT 386 at work.
Both work fine with VoXaLot.
This afternoon from the office I have tried to call at home using prefix *031 followed by my VoXaLot number. The destination phone rings, but when my wife takes on the handset, she hears nothing, even if I am able to hear her voice. Notice that calling at home using my PSTN number, I have no sound problem at all.
I appreciate any help/suggestion.

Update: the problem raises only calling from HT 386 to C450IP. When the call is made from C450IP to HT 386 all is OK.