This is definitely one of the highlights of today's Nexus 7 presentation for me: multi-network LTE support in one device. No mucking about with carrier-specific models. This is really great, assuming your carrier is supported.
The new Nexus 7, if you opt for the LTE model, will support LTE data connectivity on AT&T, Verizon, and T-Mobile. That's just kind of awesome. There are some potential caveats, though. Google did not elaborate on which frequencies were specifically supported, or if 3G support would be available on all three networks.