Hi, Onderchick. According to the Stonyfield Farms website:
"[t]he cultures become dormant when frozen, but once thawed either in the refrigerator or by your body heat when ingested; they will become live and active once again."
P.S. Not that you asked, but if you are looking for an amazing yogurt, try Greek yogurt. Stonyfield Farms makes a good one (called Oikos), but my favorite is Fage 0% (non-fat, plain Greek yogurt). 9 oz has 90 calories and has 15 grams of protein. I add a bit of honey or agave nectar to mine. I eat it every single day and am absolutely addicted.
I spent a summer eating all my yogurt frozen once... was living in a dorm room with a mini-"fridge" that froze EVERYTHING even on the warmest setting. I loved it!
Also, that's good to know about the bacteria. I know some bacteria recover from freezing better than others (I'm a biochemist, I freeze bacteria in the lab all the time!) but I never thought about the ones in yogurt.