Really we have no way of knowing how many; there could be many hundreds of happy users like Fred out there [and thousands like me still trying to tame the !*$%* bitch]. Lacking Will's expertise I have have had nil success using the pjsua CLI for anything, except breaking things, and without PSip I'd be straight out there looking for a different VoIP client. [Erm ... any suggestions?]What about psip, my guess is that at the moment it has less than 20 users and some of these are because they are experimenting with it. Maybe it deserves to stay in for another release to give it an opportunity to mature. Just including the commandline pjsua instead would probably save 200KB in all the scripts and icons that are needed to run the gui.
Yes, it would be useful to have a buddylist of those happy to help people test PSip and yes, the privacy issue is important. Maybe a transient wiki-type list would be the way to be heading on this one.