Teams with Third Party device

Hi.

Is it possible to leverage teams as a "SIP Trunk" provider, or use a single user account with a third party desk phone?

The reason for this would be to provide a couple SIP trunks to an onsite phone system which has SIP capabilities (Yeastar P series). 

I keep looking at provisioning phones, but it requires codes to be generated and entered, and I was hoping there would just be some standard SIP credentials available, such as the SIP domain name, username and password.  This is all that is required to register a SIP Trunk usually.

Is this possible at all?

There are already many teams phone accounts in operation on the tenant, but one site has an existing phone system which is able to make internal extension calls just fine, but currently has no external calling available due to SIP trunks being cancelled by the owner.  They had hoped to use Teams for the trunks.

Thanks.