WHAT IS THE MICROSOFT TEAMS SIP GATEWAY?
The Microsoft Teams SIP Gateway became generally available in December 2021, allowing SIP registration to Microsoft Teams using compatible desktop handsets allowing core Teams calling functionality. This functionality is provided at no additional cost (assuming accounts are licensed for Microsoft Teams and Phone System), allowing organisations to utilise existing fleets of legacy handsets with basic Teams calling functionality. It is noted that you are not going to get the full functionality that Teams calling can provide via the SIP Gateway, if you need support for features like call queues, video calls, calendar integration, address book search, I would recommend sticking with a Microsoft Teams Certified device.

Setup and registration of devices for the SIP gateway follows familiar processes if you have used remote provisioning services for Skype for Business certified handsets before, the main configuration change will be updating the device provisioning server URL in DHCP. Sign in of the devices is done by utilising the https://microsoft-com/devicelogin URL via the code presented on the handset device, or bulk provisioning from the Teams Admin Centre via MAC address upload (although this still requires a code physically input into the device). There are a few other steps to be aware of, that will be covered in this article.

It is also worth noting that Microsoft Teams SIP Gateway is a different service to the 3PIP gateway. Currently Skype for Business certified IP phones can be used to sign into Microsoft Teams and be used with limited functionality (this limited functionality is comparable with the current limited feature set of the SIP gateway). However, Microsoft have previously stated that there will be no feature additions to any Skype for Business certified devices going forward. The support for 3PIP phone with Microsoft Teams was due to be retired on the 31st of July 2023 but has now been extended beyond 2023 with no official date given yet.

Regards,
Jimmy

I think that is a good course of action run 3, I've thought of something similar before, though not as thoroughly as you have. I value the time you took to share your knowledge with me, as it has been invaluable to me in my career and personal endeavors.