
This device was the CPE for their long-dead T-Mobile@Home service. While that service is not longer offered, it remains functional. My brother-in-law still has the service locked in at $10/month.
The fact that these devices remain available is a curiosity. T-Mobile still supports UMA calling. That makes me wonder if they could be used in some novel way around the house. I have too many unfinished projects already, but these do seem interesting.