Ask HN: What's going on with T-Mobile numbers and fraud?

Is there a new variant of click/install fraud using T-Mobile?

Some of my clients, largely startups, are seeing over 50% of US users on T-Mobile numbers at a time when T-Mobile's market share is less than 25%. I haven't seen a large skew by demographic, and samples from third-party data brokers don't report suspected bot activity or unusual app registration patterns on these numbers.

Meanwhile Elon is taking international SMS fraud seriously enough that he's killing SMS 2FA at Twitter, and Facebook seems to be following suit to a degree.

What gives? Are other people also seeing strangeness around T-Mobile users?