Same. It's got some real bugs. So after my phone was just updated today with the newest version of graphene. Here is what I discovered. This feature works when it wants to. I tried calling my landline 5 times in a row, every time i answered the other line and only once did the RTT button on the bottom left disappear and was replaced with a record call button. When I did click the record button it worked as expected, and the file was indeed created in the correct location. Then I tried inbound....same results but this time it worked 2 times out of 5 calls. Finally I called another cell - took 6 tries to get the rtt button to go away and call record button to show.
It needs work, but VERY happy to see this.