T-Mobile claims they are only doing this on traffic pumped numbers that cost them significantly more than that to call, but from the little I've looked into it

T-Mobile claims they are only doing this on traffic pumped numbers that cost them significantly more than that to call, but from the little I've looked into it they're charging this fee on paid conference call numbers that cost $0.002/min to call in the ratedecks I've checked (after doing an LRN DIP of course). I've reached out to T-Mobile's business team repeatedly on an account that I'm a POC on to get a full list of surcharged numbers, but they are unwilling to disclose this basic information. This kind of stuff is what keeps businesses on Sprint and Verizon, at least they know their NANPA calls will get delivered reliably without surprise surcharges!