The old "Verizon iPad" was already the most versatile: It would work with AT&T, T-Mobile, and Verizon.
If you purchased an AT&T or T-Mobile iPad, it would only work with AT&T and T-Mobile.
This development means there's a single model, and they all work on all four major carriers. *And*, the pre-installed SIM works on three of them, without having to get SIMs for each and swap them in.
Ah I see. Okay. I wasn't aware about the AT&T or T-mo iPads. Well good that Apple fixed that. iPads should've never carrier specific from the get go.