Native bridge of the media stream doesn't work with some versions of the Grandstream firmware. (It's important to me because I have an instance of Asterisk at the end of one DSL line, and Grandstream phones on two other DSL lines - when calls are made between them it's much lower latency if the media stream is direct.)
Known not-working version of the firmware: 126.96.36.199
Known working version of the firmware: 188.8.131.52
There still seem to be issues with the "hold" and "flash" buttons - the media stream is redirected back to Asterisk when either of these buttons is used.
Any other information available?