Buying guide: Which iPhone should you get?

While there are many dozens of Android phones on the market, Apple to date has released only five models of the iPhone. Only three are currently offered by Apple and its U.S. carriers ( AT&T, Verizon, and Sprint). Whether you’re planning your first foray into the world of iPhone ownership, or an upgrade from a now woefully outdated first- or second-generation model, choosing which iPhone to buy is a decision that requires some thought. Your options: The iPhone 3GS, the iPhone 4, and the iPhone 4S.

Cash as cash can

The first question, as it so often is when it comes time to buy shiny new electronics, is what your budget is. In theory, if you’re buying your new iPhone for yourself, you’re prepared to set aside at least $70 per month for service (and possibly considerably more, depending upon your service plan). Each carrier sells new iPhones with two-year contracts, so whichever iPhone you get, remember that you’re paying at least $1700 over the next two years to use the device.

But your phone’s contract cost is non-negotiable. Where you can save some cash—if you’re willing to sacrifice in other areas, as we’ll discuss below—is on the one-time expenditure you make when you actually buy the phone itself.

The iPhone 3GS is available for free from Apple’s online store, though you’ll have to sign a two-year contract with AT&T to get that 8GB model at no cost. (Apple sells an unlocked version of the 3GS for $375.) AT&T is the only carrier to offer the 3GS, as that phone is only compatible with AT&T’s GSM-based network. (Curiously, AT&T lists the iPhone 3GS for sale at $1, though as this article was published, AT&T’s online store claimed to be out of stock.)

Bargain hunters who’d like a phone released after 2009 can still save some coin by opting for an 8GB iPhone 4. It costs $99 with a two-year contract, which you can sign with either AT&T, Sprint, or Verizon. (Unlike the iPhone 3GS, the iPhone 4 works on the CDMA network used by Verizon and Sprint as well as AT&T’s GSM network, though you have to buy a phone compatible with that specific network.)

Then, there’s the latest iPhone model—the iPhone 4S, which came out in October. It starts at $199 for the 16GB model, with 32GB and 64GB versions available at $299 and $399, respectively. Again, those prices require a two-year contract; you’ll be able to choose which carrier—AT&T, Verizon, or Sprint—that you sign up with.

What’s in storage

If money is no object, your next must-answer question applies to storage. As noted above, the free AT&T iPhone 3GS and the $99 iPhone 4 are both offered only in 8GB models. And the phone’s operating system and stock apps eat up some of that storage anyway; you’re probably looking at no more than 7GB of usable storage with one of those models. Is that enough?

That depends. Will you be syncing your iTunes music library with this iPhone? If the answer is yes, check how much music you own by clicking on Music in the Library section of the iTunes sidebar and then looking at the status line at the bottom of the window. If you’re using iTunes Match, you can obviously free up plenty of music space, since most of your music will instead reside in iCloud, not on your device.

If your music library won’t be a problem, consider what else you might use the iPhone for. Many apps are on the smaller side—well below 50MB. But if you’re an avid gamer, remember that graphically intense games can gobble up 600MB or more in an instant. And if you plan to take oodles of photos—or shoot hours of video with the built-in camera on your phone—that’s another big potential space-eater.

Remember that the iPhone 4S comes with either 16GB, 32Gb, or 64GB—plenty more storage, if that’s what you need.

Feature show

On the hardware side, the 3GS is available in black only and sports a rounded back. The 4 and 4S are available in both black and white, and sport a straight back. You can still find cases and accessories for all three models, but accoutrement for the 4 and 4S are more readily available.

All three models support iOS 5, Apple’s latest and greatest incarnation of its mobile operating system. But there are significant differences among the three iPhones in terms of what they do and how they do it.

Cameras: Each can take photos and shoot video. The iPhone 3GS is limited to a single 3-megapixel camera and shoots VGA-quality video. The iPhone 4 employs a 5-megapixel still camera that can shoot 720p HD video, and a second, front-facing VGA-quality camera. The iPhone 4S uses an 8-megapixel still camera that can shoot 1080p HD video, and the iPhone 4’s same front-facing VGA-quality camera. Only the iPhone 4 and 4S support FaceTime, Apple’s video-calling technology for calls between iPhones, iPads, iPod touches, and Macs.

In plain English, the iPhone 4S can take point-and-shoot quality photographs, the iPhone 4 shoots decent photos, and the iPhone 3GS takes photos with a decidedly camera phone-esque veneer.

Processors: Camera quality isn’t the only way the iPhone 3GS, 4, and 4S compare along a good, better, and best scale. The phones’ internal processors mirror that line; the 4S uses the same Apple-designed A5 chip that powers the iPad 2, and it blazes. The iPhone 4 use a less-zippy but still impressive A4 processor, and the 3GS uses a measurably slower processor still. You may only notice that slowness if you’re frequently around folks using newer, faster iPhones, however.

Displays: The iPhone 4 and 4S use Apple’s Retina display, packing the screen so densely that your eye can’t make out the individual pixels; it’s a particularly impressive feature for apps written to take advantage of the Retina display. The 3GS’s display is less visually impressive, but still quite legible.

Voice Recognition: Only the iPhone 4S supports Siri, Apple’s virtual voice recognition-based assistant. Folks who use Siri quickly come to depend on it for quick tasks like scheduling reminders, setting appointments, checking the weather, and taking dictation. But the vast majority of iPhone owners have long relied on their fingers for those tasks without much difficulty, so you won’t suffer much without it.

Pick a phone, any phone

So, how do you choose? If you’re the kind of gadget hound who needs the latest and greatest Apple technology, well, then you probably didn’t just read this piece—the iPhone 4S is the only option that will satisfy you.

The $199 that separates the 16GB iPhone 4S from the 8GB iPhone 3GS could pay for somewhere between two and three months of cellular service for either phone. Whether paying extra cash for the increased storage, better cameras, additional features, and snappier performance is worth it is an entirely personal decision.

Some extra points to consider: You’ll sign a two-year contract when you order a new iPhone (unless you opt for much pricer unlocked versions of the iPhone you buy). You’ll never be able to upgrade your iPhone’s storage space size. But it’s quite likely Apple will offer another major iOS upgrade or two over the next two years, and there’s no guarantee that the already two-and-a-half-year-old iPhone 3GS will support any or all of the features of a hypothetical iOS 6; 2008’s iPhone 3G, for comparison’s sake, can’t run iOS 5.

Spending $99 for the iPhone 4 instead of taking the free 3GS may thus provide a better return on your investment, since you’re under contract with your carrier anyway. It’s a better phone in numerous respects, and will very likely be able to run at least one iteration of iOS that the 3GS cannot. Saving an extra $100 by eschewing the iPhone 4S today might make it easier to justify purchasing a hypothetical future iPhone once your new contract is up two years from now.

If, on the other hand, you’re considering a new point-and-shoot camera, or you’re apprehensive about your potential skills as a literal touch-typist, the extra $100 for the iPhone 4S may be worth it.

Regardless of which phone you choose, the good news is simple: You’ll end up with an iPhone, and that means you’ll have an excellent smartphone in your pocket.

[Lex Friedman is a Macworld staff writer.]

Updated 11:23 a.m. ET to correct an error in describing the iPhone 3GS’s processor.