When I phone T-Mobile via 611 from my cell, the support reps do not have access to my phone number and cannot even tell if I am calling from their own network. Try it, they ask for the number every time. Why does T-Mobile not have inbound caller ID? This lack of such a basic capability does not inspire confidence.
They have it. It recognizes my number when calling in and the wait times are long enough to trigger the call back option. When you are transferred over to a representative at one of many call centers. That information might not show up for the CSR.