Also consider that T-Mobile as it exists is the result of years/decades of mergers and acquisitions so they have decades of legacy and non-conforming systems. This situation is bound to cause security issues as well. I had a family member work for an MVNO that interfaced with them and this is what she saw.
>"Also consider that T-Mobile as it exists is the result of years/decades of mergers and acquisitions so they have decades of legacy and non-conforming systems."
This is true of just about every single mobile carrier today. In fact this is true of all telecom companies for most of their history from mobile carriers, to cable companies to ISPs. The entire telecom industry is an unending series of consolidation and acquisition of assets. This is already 12 years out of date but this should give you an idea:
