I used the cyt35.exe tool and have successfully unlocked the ip8100 and have it working with asterisk for
dialin/out...but there are some problems.
  The command line was "cyt35.exe VTECH". You have to login to the web interface of the ip8100 for the tool
to work. It seemed to take forever, but leave it alone and wait for the cyt tool to give you a success/fail 
message.
  The only problem I'm having is that the status light goes from green to amber and I can't login via http 
or ssh and get 25% packet loss when pinging. I pull power to reset the base and everything works again. This seems to
happen within 24 hours of resetting, but I haven't had time to figure out exactly what is going on. I'm going to
setup pingplotter and reset it, which will at least give me the time to failure. I have setup the ip8100 to log to
my asterisk boxes syslog server, but it only logs voice events. The provisioning server is set to http://127.0.0.1
so I don't think this is a phone home to vonage problem. It's running Firmware Version: 11.4.0-r060330.
  I got a pretty good deal via ebay, but would say if you were buying new, get a wifi phone. The price 
difference will get you much more phone functionality. There aren't any special keys to use on the handset and it only displays
caller id. There isn't anyway to address a handset display or page via asterisk, from what I can see.
  I give it a 7 out of 10 overall.