Data Networks and Your iPhone
You can't typically make or receive phone calls on a wireless phone without tapping into a cellular network. And you can't prowl the Internet (or send email or messages) on a mobile phone without accessing a wireless data network. In the United States, the iPhone works with Wi-Fi, EDGE, 3G, and the various 4G, or fourth-generation, networks, the fastest of which is known as LTE (Long Term Evolution).
In the United States, Verizon Wireless was first out of the gate with LTE and has the most built-out network. But the other major carriers AT&T, Sprint, and T-Mobile also have an LTE footprint, with Sprint in particular still a relative LTE newbie. If you're cruising in the fastest cellular lane, you'll see the small LTE indicator at the upper-left corner of your phone.
Confusingly, if you are not in an LTE area but are instead tapping into another 4G variant called HSDPA+, you will see the 4G indicator instead of LTE in the upper-left corner of the phone.
The since-discontinued iPhone 5 was the first LTE-capable iPhone. The phones that replaced it, the 5c, 5s, 6, and 6 Plus can support more than a dozen different LTE bands around the world, including some ultra-fast variations.
But you're not always going at or near top speeds. The iPhone is also compatible with slower Verizon and Sprint 3G CDMA networks. (And it works also with another wireless technology, Bluetooth, but that serves a different purpose.)
The iPhone automatically hops onto the fastest available network, which is almost always Wi-Fi, the friendly moniker applied to the far geekier 802.11 designation. And "eight-oh-two-dot-eleven" (as it's pronounced) is followed by a letter typically, b, g, or n. So you see it written as 802.11b, 802.11g, and so on. The letters relate to technical standards that have to do with the speed and range you can expect from the Wi-Fi configuration. But don't lose sleep over this issue if you haven't boned up on this geeky alphabet.
For the record, because the iPhone 5 and later adhere to the 802.11a, 802.11b, 802.11g, and 802.11n standards (plus 802.11ac on both iPhone 6 models) as well as the dual-band 2.4 GHz and 5 GHz spectrums you're good to go pretty much anywhere you can find Wi-Fi.
These days, Internet hotspots are in lots of places: airports, colleges, coffeehouses, libraries, public parks, and elsewhere. If you have to present a password to take advantage of a hotspot because it costs money or you have to authenticate your credentials, you can enter the password by using the iPhone's virtual keyboard.
Still, Wi-Fi isn't ubiquitous yet and neither is 4G, which leads people, at times, right back to CDMA or EDGE or 3G. EDGE is shorthand for Enhanced Datarate for GSM Evolution (good to know only if you're on a million-dollar game show) and is based on the global GSM phone standard. And 3G stands for third generation; 3G websites typically download two times faster than EDGE, and sometimes even faster. But, again, Wi-Fi downloads are even zippier.
The bottom line is this: Depending on where you live, work, or travel, you may feel like you're teetering on the EDGE in terms of acceptable Internet coverage, especially if Wi-Fi or true 3G is beyond your reach. Even worse is when your iPhone shows No Service, but the picture is indeed brightening. Wi-Fi and 4G networks are in more places than ever before. And the iPhone not only loads web pages a lot faster but also manages to do so with longer-lasting batteries.