Cannot sign in to a Poly CCX 500 desk phone with the Teams SIP Gateway

I don't think it's fair to lay the blame entirely at Poly's feet. They built the device to Microsoft's specifications, and Microsoft certified it. Almost immediately, Microsoft allowed the app to get too bloated to run well on the device. Instead of working with Poly to address the issues, Microsoft barged ahead with adding new features.

We support the community offices of the elected representatives for the citizens of our province, and these users need desk phones—they need to be able to do things like place a call on behalf of a constituent and hand over the receiver. Fortunately, the SIP Gateway seems to be the answer to our prayers, especially now that there are cordless phone options available.

The ironic thing is that we bought the Teams Phones to replace our 3PIP phones due to issues with Skype for Business Online, and now we're essentially going back again.