Yes, iPhone 4S is HSPA+
There were rumors the 2011 GSM/AT&T iPhone would have an HSPA+ radio for faster download speeds but when Apple announced the iPhone 4S, while they said it would do 14.4 mbps, they only listed it as an HSPA device.
Now, some are of the opinion that anything under 21 mbps should qualify as HSPA+, so iPhone 4S with only 14.4 mbps speed shouldn't qualify. However, 3GPP release 7 doesn't mandate that faster speeds are necessary to qualify as HSPA+ -- a device can support any 3GPP release 7 feature and still be classified as HSPA+. The Qualcomm chipset in iPhone 4S uses 3GPP features, and so it's an HSPA+ radio, speed be damned.
So while iPhone 4S did indeed get its HSPA+, it didn't get the 21 mbps or 42 mbps speed to go with it that many were hoping for. Also, Apple chose to neatly sidestep the whole 4G/fake 4G issue, so we won't open that can of worms here either.
Note: This applies only to the GSM/AT&T iPhone 4S. The CDMA/Verizon/Sprint iPhone 4S retains the same EV-DO rev A