Which carrier(s)/MVNOs plans that work with the 3G Nexus 7? Please share. (US)

We know about AT&T own data plan/shared data plan as Google bundled the SIM with the 3G Nexus 7, but what about others?

T-Mobile's $30 4G monthly plan: doesn't work. Looks like T-Mobile blocks it. The N7 will as for "network sign-in" that brings you to my-t-mobile website, but then it doesn't work.

Straight-talk AT&T: works, for now. Had to pick ATT broadband APN and reboot the N7. Seems to have unreliable connection though, at least for me, as it takes quite a while to connect. Not sure how long this would last either.

Those are the only two that I have personally tried. Anybody? How about the various MVNOs? It's sad that T-Mobile put a restriction on this