To register third-party SIP handsets with Microsoft Teams using SIP Gateway, two primary actions are required. First, the ability for users to make calls from SIP devices must be enabled within the organization's Teams calling policies. This is achieved by setting "SIP devices can be used for calls" to "On". Second, the SIP handsets must be directed to the SIP Gateway service for configuration and registration. This is done by setting the device's provisioning server URL to the appropriate regional SIP Gateway URL provided by Microsoft.

A: Configuration profiles in the Microsoft Teams admin center are used for managing native Microsoft Teams devices, not for third-party SIP devices connecting via SIP Gateway.

B: While enabling the voice calling policy is a necessary step, LLDP (Link Layer Discovery Protocol) is not the mechanism used for SIP Gateway provisioning or registration.

C: Configuration profiles are not the correct tool for SIP Gateway devices. The specific detail needed is the provisioning URL, which is the standard method for these devices.

1. Microsoft Learn. "Configure SIP Gateway." Microsoft Teams Documentation.

Section: Enable SIP Gateway: "In the left navigation

go to Voice > Calling policies. Select a policy or create a new one. ... turn on SIP devices can be used for calls." This supports the first part of the correct answer.

Section: Configure the provisioning server URL: "You can set the provisioning server URL on the device's configuration screen or by using the device's web administration page. ... Use one of the following SIP Gateway provisioning server URLs depending on the location of your device: EMEA: http://emea.sip.skype.com..." This supports the second part of the correct answer.

2. Microsoft Learn. "Plan for SIP Gateway." Microsoft Teams Documentation.

Section: Onboarding and provisioning: "SIP Gateway supports provisioning SIP devices from the Teams admin center. ... For bulk provisioning

you can upload the MAC addresses of the SIP devices that you want to provision." This process is initiated after the device is configured with the provisioning URL to contact the service. The document does not mention using configuration profiles or LLDP for this purpose.