At the time of writing (February 2023), SIP Gateway support for Analogue Telephony Adapters (ATAs) is in public preview. After the feature is launched you should check the documentation for any updates or changes. The video posted below is a short overview of the main steps needed to register an analogue phone to Microsoft Teams via an ATA. It is currently anticipated that AudioCodes, Cisco and Poly ATAs will be compatible with Sip Gateway.
Microsoft engineering is investigating how to support bulk installations. Look out for additional details when ATA support goes to GA.
Since I posted the video, replacing the caller ID with a Service Number has been superseded by assignment of a Resource Account. See the screenshot below. Service Number support for CLID policies will be depreciated.