I am using the nymgo VoIP service with the MizuPhone.

A nymgo test call goes normally until the playback begins. During the 10-second playback period, a strange sound is played back, that sounds like a low-frequency stuttering human voice. At first I thought it to be a distorted version of my recorded message. However, after repeating the test with complete silence following the beep signal, it was found that this 'sound' occurs regardless of whether or not there is any audio input during the recording period of the test call.

This is both under Windows 2000 Professional, and Windows 7 Professional (on the same hardware, but using a dual boot).

With the phone running on a different computer (an Asus netbook running Windows XP Home Edition) the phone performs the test call perfectly normally. That is, if one records voice, it is reproduced, and if one is silent, there is silence, and the playback is normal and of good quality.

Both systems are using the same wireless router-modem. It is the same whether using a hard-wired (ethernet) connection, or the Wi-Fi signal: the desktop system fails, the netbook succeeds, as described.

The Mizutech softphone can switch between primary and secondary audio configurations. I have Realtek HD audio set as the primary configuration, and the default MS Windows audio playback and record as the secondary. It makes no difference whether the primary or secondary is active: the playback fails, as described. It is something peculiar to the desktop computer, apparently.

I thought it might be the ethernet port, so I plugged a USB Wi-Fi adapter into the desktop unit, and tested the MizuPhone through that. The adapter creates its own port, separate from the ethernet adapter. The problem, however, was the same: inability to properly play back at the appropriate time during the test call.

I can't think of where to look next. Has anyone else ever come across this or anything resembling it? What in the system could be doing this?

P.S.: the proprietary VoIP protocols (e.g., Skype and Yahoo! Voice) work fine, on the first try after installation.

P.P.S.: MizuPhone v2.1.1.14

Yes, and thank you for the reply. 

I apologize for the delay in responding to your offer to help.  For some reason I missed the forum's notification in my Inbox, until I happened to check the forum directly, and only then saw your reply.

Give me a day or two to work on generating the file you are requesting.  Thanks again.

Problem has been resolved.  For benefit of other mizuphone users seeing this thread in a search:

The nymgo VoIP service apparently relies on a codec unsupported by the free version of mizuphone.  Tech support asked me to download the non-free version of mizuphone, because in their tests (apparently, using the non-free version) they were unable to duplicate my inability to communicate.

I followed the directions, installed the paid version (unfortunately, it immediately came up as 'expired') and in the single minute of operation allowed by this version, I was able to make a test call to nymgo, which worked perfectly. 

Thanks to mizuphone support, and its excellent technicians who were able to diagnose the problem from my description alone, as the log they analyzed showed no evidence of any connection difficulties. 

As well, for future reference, both I and readers of this thread will know how to identify a failure due to incompatible codecs, and how to resolve it.