Jeff Pulver revealed that Xten knows when you use its software to make VoIP calls.
While I don't know how much of a privacy issue this raises, since the phone company knows each time you make a call currently, I am wondering what security issues that raises, based on the data being transmitted.
For example, do they know the IP address you're located at? Do they know the duration of the call? What number (sip or pstn) that was dialed? What information are they collecting? Or is it simply, a becon that hits a counter saying "another call has been made using XTen software." The latter is not a big deal in my mind and equal to a hit counter that no one sees on web sites.
P.S. Xten now has a Mac client too that works specifically with Vonage.