As far as I’m aware (and I’d hope I’m up to date here) that’s only possible if you’ve logged in to your account, so they’d have your name/etc.

Matching a cookie to individual names is not instantaneous and would be very expensive for someone at t mobile’s scale to do every time a session started.

Some b2b companies do something similar where they can match your ip to a list of known corporate ips to find where you work in real-time, but that’s pretty expensive.