Can the Nexus 7 send and receive GSM texts and calls?
Yes and no. The hardware is capable of sending/receiving GSM calls and texts but there's no way to do with via the stock software. I doubt any after market app would do the trick either, as it appears that tweaks need to be made at the OS level.

There are a couple of devs working on this on XDA. There's no eta, but they should get it done in time. We can only wait.

http://forum.xda-developers.com/showthread.php?t=2025377