call disjoint when client side playing Music on Hold

[yiuyiu]

every time I calling to my friend (outside number) and the line will be "disjoint" after he hold the line...after he pressed a hold button, I only hear a music on hold for a while and going to silent...

Checked with the system, the call was not dropped but we cannot talk to other side...

So that I did the trace and I found that every time I loss the sound, below line will show on the trace result…

Start Modem PassThru aux:none tone:none from voip:IP Address

Does anyone have a same problem? Dose anyone know the meaning of the trace line?

This problem makes me crazy and it is starting complain from other people...

Thanks in advance