Posting a follow up to close the thread, should anyone pull this up in a search.
Turns out that a temporary account that T-Mo had provided to me while my number was being ported over (ostensibly as a customer service) hosed the provisioning of the feature after my number did port over.
As a consequence, the review of the first ticket submitted did not turn up any issues and was chalked up to user error on the CSR's part. The second trouble ticket was closed without resolution, so I'm not sure what happened there. A third ticket finally resolved the issue, but only after I called Tech Support and walked them through what happened during the initial activation of the device.
A suggestion to any others dealing with provisioning issues like this is to ask for "Technical Support" when calling 611, versus rate plan, services or billing. The IVR prompts seem indicate that this is primarily about phone problems rather than service, but the people manning the desks are helpful with any issue (and even added the services without handing me off to another CSR when the issue was resolved).
Boo to T-Mo for such poor call flow quality and failure to communicate. Hurrah to Tech Support for getting it done.