as posted above is great, a few collegues use it extensively here in Sweden.
Basically it's a VST-plug that transfers audio bidirectionally directly from your host app to/from an external party over the net.. Ie, both you and you hired VO have it running in PT and voila, you have a telephone like connection with "studio audio quality" (see below), being able to record everything in realtime to PT.
It comes in several flavours, from "Free" to "Studio". The difference lies in the supported bandwith, hence with the "Free" you only get max 128 kbps, with "Studio" up to to 256 kbit/s. The "studio" account also incorporates a "file send" function that allows you to transfer any file directly from within the host.
To me the bandwith isn't really an issue, it's good enough to hear everything you need. Just record everything locally and use DML to coach the VO Talent "live" and then just transfer the full audio files via FTP later.
The instant record/transfer feature is good, but for me not at all necessary. In a music recording context, being able to jam live with someone can probably be invaluable. For me, the most important thing is being able to give direction and coach realtime so that I know that I have the takes I need to get the job done.