I have the same problem and still have this problem.
My migration to BT Digital Voice (DV) relies on being able to serve a set of engineering building and a station gift shop at a heritage railway. I also have our main station with a number of legacy phone line based devices (faxes etc.).
At our main station and admin building I have installed a SH2 with a DECT W73P cordless phone, this supplies our customer and volunteer Wi-Fi. I have purchased Digital Voice Adapters BT X16-G90 (item code 100121) this is all the recommended BT kit, there is nothing that isn't BT/EE equipment.
I can pair X16-G90 to the W73P's base station and to my home BT DECT phone, but can't pair to the SH2 either at the railway or my one at home. In these tests, I used the WPS button on the adapter and the W73P base station. The phone has no dialing tone and can't dial out.
Coming back to pairing to the SH2 (as per the setup guide), I have tried the following:
No pairing on any of these 3 items
My setting are the default SH2 settings under Advanced wireless settings
I have not investigated the alternative Wireless Modes and in my current SH2 installation the on board
BT socket is not available to me on the SH 2's Manger phone tab (seen in the DV Adapter's User guide) is
not present either on the railway's or my own SH2.
I need advice on how to solve this from an expert (P.S. before I retired I had 40 years of IT Support & was a Network engineer), so please no FAQ pages, or applying the latest patches .