I have to admit is a little disappointed with the phone when I got it. I updated the firmware as far as it would allow me, but the more recent versions of the software would not install After a bit of googling I found that there was supposedly a procedure for updating the old firmware to one of the newer sets, but that it was a secret. That got me really interested so I dug a little deeper. I found a PDF that contained a link to a Yealink FTP server which I’m not sure is supposed to be publicly available. On the FTP server was a set of files that detailed in rather broken English the process. Basically you put the phone into a special mode that causes it to download a new firmware from a TFTP server running on the same network and off it goes with the new firmware.
My phone now says is has firmware version 18.104.22.168 and it now has all the features I was hoping to get. From what I can see it now has pretty much the same software as the new VP530.
I also tested the technique used to get root on the old firmware and it is no longer available, however the technique used for the T38G now works.