How to use an unlocked iPhone 4 with T-Mobile

Now that Apple sells unlocked iPhone 4s to U.S. customers, budget- or carrier-conscious buyers may wonder whether they can buy an iPhone 4 and use it with T-Mobile. Although T-Mobile has its own 3G network, it doesn’t use the same frequencies as AT&T’s; thus the most a T-Mobile iPhone customer can hope for in the U.S. is slower, EDGE (2G) data speeds.

Even if you’re willing to settle for slower downloads in exchange for jumping onto T-Mobile’s network with a legitimate, unlocked, non-jailbroken iPhone, there’s a bit of work involved. So I visited a local Apple Store and purchased an unlocked iPhone 4 (in white, natch) and set out on my journey. Here’s what I did to get connected.

SIM versus micro-SIM

First, you’ll need a T-Mobile SIM card. If you already have a T-Mobile phone, you already have just such a SIM card; pop it out of your phone, and you’re good to go. You can also go to T-Mobile’s website or a local T-Mobile store and pick up a prepaid or pay-as-you-go SIM card. I bought one for $10 at my local store.

There is a catch, though: The iPhone 4 doesn’t include a SIM slot. Rather, Apple uses a slimmer SIM, the micro-SIM. As it turns out, a micro-SIM is actually just a SIM that’s undergone some serious trimming.

Presumably at some point T-Mobile will realize there’s now an opportunity to reach users of unlocked iPhones and offer micro-SIMs as well as standard SIM cards. (When we called T-Mobile’s PR department, they declined to comment about the unlocked iPhone.) In the interim, then, you’ll need to make your own micro-SIM.

To carve that SIM into a micro-SIM, you’ll want to gather a few tools: your unlocked iPhone, your T-Mobile SIM card, a sharp knife (I used a box cutter), and a pen or marker. You might want a cutting board, too.

I used a paper clip, too, only to discover that Apple still does provide a SIM removal tool (it looks like a teeny, tiny dagger) with every iPhone 4. Oops. Well, if you lose it, you can still use a paper clip instead.

1. Find the slot

Locate the micro-SIM slot on your unlocked iPhone 4. It’s on the right edge and sports a tiny little hole, the perfect size for an unfolded paperclip—or that blasted SIM removal tool that I didn’t notice in my iPhone 4 box.

2. Open with the SIM tool (or a paper clip)

Use that SIM tool for what it was intended for. Or, if you’re like me, needlessly sacrifice a paper clip to the cause, and poke one end into the hole. I had to push with a fair amount of pressure to get the micro-SIM card tray to eject. Pull out the tray. If this is a brand new unlocked iPhone 4, it will be empty.

3. Trace your cutting path

Grab your full-sized T-Mobile SIM and your marker, and using the iPhone’s micro-SIM tray as a guide, trace around the edge of your SIM.

4. Cut the SIM

Now, you need to cut your SIM to micro-SIM size. The important part—the part you can’t cut—is the circuitry, and it’s really obvious: It’s the shiny part. As you cut your SIM card, leave the gold side facing you, so that you can be sure you don’t cut it.

If you cut the shiny part of your SIM card, it won’t work anymore. You can buy (and sometimes request from T-Mobile) a new one, but if all your contacts are stored on your current card, you don’t want to break yours. Measure twice, cut once. But also remember that you can always cut the card more if you leave it too big at first, but you can’t really make a too-small SIM bigger.

I traced some broad lines on my SIM card and then used my box cutter to saw deeply along the lines. (If you own an X-Acto knife or some similar weapon, you may find you have an easier time of it.) Once I sawed sharply enough I carefully used my fingers to bend and twist the SIM card—remaining, of course, exceedingly attentive to (and protective of) the circuitry—until the extra pieces snapped off.

5. Load it up

Once your SIM surgery is complete, your resized card should fit comfortably in the micro-SIM tray. The shiny part faces down, with what’s left of the T-Mobile logo facing up.

Slide the tray—with the SIM atop it—into the iPhone. If the iPhone still says No SIM after a moment, eject the tray again and try reorienting your card. In my case, the T-Mobile logo had to be oriented upside down for the iPhone to recognize the SIM.

After just a few seconds, your iPhone should successfully connect to the T-Mobile network. But—at least until the release of iOS 5—you’ll need to connect it to iTunes first. Plug the phone in, let iTunes perform its initial sync, and then disconnect your phone.

You should now be able to place calls and text messages with your iPhone 4, over T-Mobile’s network. Remember that some carrier-dependent features—like Visual Voicemail—won’t work.

The trouble with MMS

You know what else won’t work? MMS. The Camera icon for attaching photos or videos is missing entirely from the Messages app. But that one’s fixable—sort of. If you search the Internet, you’ll find various settings to tweak to get MMS working; until this week, all that information has generally been geared towards jailbreakers. In fact, in researching this piece, I contacted T-Mobile’s customer care, and the instructions they gave me for getting MMS working actually referenced Cydia, the app commonly installed automatically by most iPhone jailbreakers.

Here are the steps that T-Mobile hoped would enable me to send and receive MMS messages with the unlocked iPhone 4. Spoiler alert: It didn’t quite work.

Go to the Settings app, and choose General -> Network -> Cellular Data Network. Under MMS, set:

APN: epc.tmobile.com

Leave Username and Password blank.

MMSC: http://mms.msg.eng.t-mobile.com/mms/enc

MMSC Proxy: 216.155.165.50:8080

Leave MMS Max Message Size blank.

MMS UA Prof URL: http://www.apple.com/mms/uaprof.rdf

Then, back out to the main screen of the Settings app by tapping Network and then General, and then Settings at the top left; this ensures your newly-entered details are saved. Now, restart your iPhone by holding down the Sleep/Wake button until “Slide to Power Off” appears. Restart your iPhone by holding down that button again—waiting until the phone finishes shutting off completely first, of course.

When you restart your iPhone, the missing Camera icon should reappear in the Messages app. It did for me. But when I attempted to send or receive multimedia messages, it didn’t work. T-Mobile eventually suggested I contact Apple for support, and to Apple’s credit, the company did walk through several steps with me to try to correct the issue. Successful MMS’ing still eludes my setup, but if we figure it out, we’ll update this story.

T-Mo, Phone Home

So with the notable exceptions of 3G, MMS, and Visual Voicemail, your Apple-approved unlocked iPhone 4 should work just as you’d expect it to on T-Mobile’s network. You can install apps, sync and update with iTunes, and—in many ways, most importantly—pop in an international micro-SIM if you travel outside the country.

[Updated at 4:21 p.m. PT when Lex discovered that he did have a SIM removal tool in the iPhone 4 box after all.-Ed.]