Release 2023.5 of Home Assistant introduced the new Voice over IP integration that enables talking to the HA voice assistant using a regular (analog) phone. The instructions currently only apply to the Grandstream HT801 and HT802 analog phone adapters. After some trial and error, I managed to call Home Assistant from a SIP phone registered on my FreePBX VoIP server. Continue reading for more details on how to configure this in FreePBX.