Now that your chances of getting a Nexus 4 are down the drain (at least for now), if you poke around the Google Play Store a bit more you may find something interesting. The newest model of the Nexus 7, the one with HSPA+ data, is now listed as "Unlocked + AT&T SIM", rather than just "Unlocked". Reading through the specs you see that Google is directly promoting the use of the Nexus 7 on AT&T's "DataConnect" tablet plans, which let users choose both prepaid and postpaid options, as well as the ability to add the Nexus 7 to a Mobile Share plan.
This is certainly interesting considering that the Nexus 4 is being launched together with T-Mobile, and the Nexus 7 supports frequencies for T-Mobile as well. The good thing is that the SIM shipping in the box doesn't cost you anything extra, and you can easily remove it and use a T-Mobile plan instead. We're curious to know why there's no official support for a T-Mobile SIM out of the box at the time of order, though.