Hmm, the plan I have looks nothing like that. I have to login to AT&T Business Direct Premier for my account, which may be why.
Mine shows:
Data Unlimited for iPhone 4S
GPRS WAP UNLTD DOM - CMB1
But I have read a few posts on Google searchs that say 4G/HSPA+ requires SOC code of HSDPPB instead of CMB1? Not sure if this is relevant to iPhone though.