There used to be an internal site from one of the carriers (I think AT&T) that gave really good info-- it wasn't intended for public use, but was public facing until they limited access.
While PhoneCarrierCheck identifies my checked number as T-Mo, I believe the other site would have identified Mint.
also ID's the same Mint # as T-Mo, and includes SMS and MMS gateway info, and whether the number is landline or wireless.
Wow - great info - thanks for sharing this stuff !!
The one Isamorph gave us is way cool because not only does it work - but is a very simple way to get such info on a batch of numbers at once...
The one shared by KentE is more polished as it gives the email-to-SMS & email-to-MMS addresses (but only for 1 number at a time).