We have been working with one of customer who uses MS Teams and they bought Bria Teams and ran into a problem you identified. In working with Bria our customer was given the following process to follow for setting up the pools described above by @shamesaaron :
If you are setting up device pooling for all users (as in, all users will have multiple devices that each have their own sip credentials) please skip to step 2. If you are setting this up for only one user, please start with step 1.
Make a new Voice account that is the same as the other one by going to the Voice and Video tab, and clicking the + button to add a new configuration, then adding all the same settings as the first one to it. This will be the configuration that uses device pooling.
Under Voice and Video, click "Edit configuration" on the configuration you wish to have device pooling turned on. In the configuration go to the Service Compatibility Options tab
Click the This service requires a different username for each SIP registration button, and also checkmark the This service requires a different password for each SIP registration button which will appear after the first it checked.
Save and Close
Go to the Team Member tab and click on the user with multiple devices. If you set up a second Voice Configuration, you will need to change the voice configuration for them to the new one.
You will now see tabs for each SIP registration, enter the SIP registrations in each tab.
Click Save and Close
On every one of the user's devices, Log out of Bria. You will want to start with Bria signed out on every device.
One at a time, log in on Bria. The first device to log in will take the first registration you set up, the second one will take the second, etc, until they are all assigned.