Beyond an icon change, what does the recent AT&T iPhone 4G upgrade mean in the performance department? For those not in the know, the new iOS 5.1, which Apple announced at yesterday's event, when installed on an AT&T iPhone 4S upgrades to 4G, as the photo above via MSNBC's Rosa Golijan shows. This has lots of people excited  on Twitter, since it feels like a free upgrade from 3 to 4. And since higher numbers generally mean better things, this must be good, right? Well, not exactly. 4G is different than 3G, but it's also different than the 4G LTE that Apple will offer with the New iPad. Here's how it all shakes out.

What do all these Gs mean?

This all has to do with data rates. The better the G, the faster the phone, theoretically. Nurdology has a technical breakdown of the actual rates that these networks boast. Here's the important comparison: 3G datarate maximum is 2 Megabits per second vs. 4G datarates can reach upwards of 20+ Megabits or 2.5 MegaBytes.

So 4G is that fast new network we've been hearing about?

Not so fast. That's 4G LTE, which runs on a different network than 4G and 3G phones. It runs much faster than 3G and 4G devices, at least according to this test via Wired.

This update is still upgrade, though, right?

Not really. This 4G network isn't that much faster than 3G, in practice, as Buzzfeed's Matt Buchanan notes. "It's slightly faster than AT&T's older 3G network--theoretically, you can reach speeds of 14.4 megabits per second on an iPhone 4S. So it's faster than what's possible on an iPhone 4 or 3G, yes," he explains. "But not much faster, in practice. It's not a generation ahead."

And the iPhone was probably already running at those high speeds yet, this is more of a marketing play, adds The Verge's Nilay Patel. "Owners of the iPhone will notice no difference in performance or data transfer speeds; the device will not magically connect to AT&T's shiny new 4G LTE network," he writes. "It will simply receive a deceptive labeling change that allows AT&T to market the iPhone as a 4G device against competitive phones from Verizon," he continues.

So, nothing at all changed?

Well, not nothing. "AT&T has rolled out a nationwide HSPA+ network, and they refer to this high-speed network as 4G," an Apple spokesperson told Patel. But, the 4S already ran at speeds that phones with the official 4G moniker reach, Apple's president of Worldwide Marketing Phil Schiller claimed when the phone first came out last fall.