I wanted to make this post to help clear some of the confusion that AT&T may now be causing to some iPhone 4s users. But in order to do this I need to give some information about 3G and 4G.
The 3G and 4G names are supposed to follow a specific standard and right now none of the carriers have the speed required to really be called 4G. However when Sprint and some other carriers got their HSPA + network that was faster than 3G they decided to call it 4G. Then Verizon brought us their LTE network and decided to call THAT 4G LTE. The LTE Network is a lot faster than the HSPA + network (so far) and the HSPA + network is quite a bit faster than regular 3G.
Things do get a lot more confusing than that but I'm trying to simplify the general idea.
For a while now AT&T has been calling a lot of their Android phones "4G" phones. However now AT&T has it's own LTE network and they are calling those phone "4G LTE". So now they are making it confusing because it's either 4G or 4G LTE.
With the iPhone they had never marked the network as being 4G, they still just called it 3G. Not sure why. In an attempt to set their iPhone 4s apart from Verizon they are now calling the new iPhone 4s a "4G" phone as well. This is because Verizon doesn't have a HSPA+ network, so the iPhone 4s on Verizon does run slower than the iPhone 4s on AT&T.
I do wish however that they'd stop confusing people and they'd just call it 3.5G or 3G+ or something like that.
So when you see that your iPhone 4s is now 4G, don't go thinking that you got an upgrade. You are in the exact same network as before getting the same speeds that you used to.
I should mention that The new iPad WILL be an LTE device for both AT&T and Verizon, although sadly those are pretty different networks even though they are both LTE and it will require you to buy a new iPad for either Verizon or AT&T, one will not work on both, unless you want just regular 3G speeds, then one should work on both.
Hope this helps clear up any confusion.