Probably 3.0+, that's my guess. I'm not sure you can really tell anymore.
Box codes are still being used on most packaging. Recent reports indicate that the Asian markets have started seeing 3.01 and above preloaded; so far, other markets haven't.
Determining PSP firmware using box codes
I bought a white TA-082 with 2.71 from GAME less than a month ago. Just ask before you buy if you could look at the box (like I did)