This is normally Brian's beat but with him busy putting the finishing touches on his review of HTC's One, I thought I'd help out. We're still seeing (and hearing) a lot of confusion about what T-Mobile announced earlier this week with regards to existing and future iPhone support on its network. Brian already went through all of this in his excellent article on the topic, but seeing continued confusion I thought I'd whip up a few diagrams to help explain.

For the purposes of this article I'm focusing on compatibility for the current AT&T iPhone 5 (hardware model A1428) as well as the new unlocked iPhone 5 (also hardware model A1428) that will be shipping start April 12.

The easiest question to answer is will existing AT&T iPhone 5s that have been unlocked work on T-Mobile's recently deployed LTE network. The answer is an emphatic yes. The original AT&T iPhone 5 was designed to work on LTE band 17 (700MHz) and band 4 (1700MHz), a superset of T-Mobile's LTE deployment (band 4). If you're in one of the few areas with T-Mobile LTE service and an existing unlocked AT&T iPhone 5, the combination will work just fine. Apple will need to release an updated carrier bundle (.ipcc file) for the phones, which I assume is coming soon - but there's no hardware change required.

The new unlocked iPhone 5 that will be available via T-Mobile doesn't add any additional functionality in this case. As you can see, both A1428 revisions support the same LTE bands.

Where it gets somewhat complicated is in the 3G WCDMA discussion. I emphasize somewhat because it's really not that hard to understand. The complexity comes from the fact that there are a number of names and acronyms here that aren't well understood by most who aren't of Klug-descent. If we focus on the frequency bands themselves and ignore their common names, things are a bit easier to understand.

The original AT&T iPhone 5 supported 3G operation on band 5 (850MHz) and band 2 (1900MHz). Only band 2 overlaps with T-Mobile's network. The problem with 1900MHz on T-Mobile is that the majority of that spectrum is used for 2G and hasn't yet been migrated over to 3G. The bulk of T-Mobile's 3G currently exists in band 4 (1700MHz uplink, 2100MHz downlink), which isn't supported on the existing AT&T iPhone 5.

After April 12th, the new unlocked A1428 iPhone 5 with band 4 WCDMA support will begin rolling out and should have much better coverage on T-Mobile's 3G network as a result. The diagram and toggles below help illustrate this:

The original A1428 iPhone 5 lacks band 4 support, which means it'll only support WCDMA on band 2. The only problem here, as I mentioned above, is that T-Mobile's 3G deployment on band 2 isn't ubiquitous - so in many cases you'll fall back to 2G/EDGE speeds. The new iPhone 5 simply enables band 4 WCDMA support.

There's one other benefit to the new iPhone 5. DC-HSPA+ (42Mbps max downlink) is now supported on all bands as well. Although it was never (and likely will never ever be) used by AT&T, DC-HSPA+ was a feature of the iPhone 5. T-Mobile on the other hand does use carrier aggregation on WCDMA in some markets and the new A1428 will benefit from higher speeds in those situations. 

That's it.

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  • Devfarce - Friday, March 29, 2013 - link

    I respectfully disagree. Not questioning Apple's legal department, however if you look back to the 4S where there was one model that was provisioned via software for CDMA+GSM or just GSM. There had to be additional licensing for CDMA technologies on the Verizon phones even though the AT&T version is technically capable but it wasn't used.

    Now since TMo USA is one of only carriers in the world to use AWS bands, I find it hard to believe that Apple would license this technology for all A1428 handsets. My assumption is that AWS implementation of DC-HSPA+ is patented and licensed for TMo A1428.

    Around the release of the iPhone 5 TMo also said it didn't need the iPhone and had something along the lines of irreconcilable differences.
  • DryCty - Friday, March 29, 2013 - link

    Let's assume for the sake of argument that you are 100% correct. Let us also assume that the added licensing fee is egregiously high - say $1 per handset.

    Since the iPhone 5 launched Apple has sold roughly 85 million iPhones - that's all models aggregated. We'll give them a generous 50% sale through mix on the 5 itself which puts us at 42.5 million iPhone 5's. Even that is over sating it because many of those were the A1429 NOT the A1428 in question. Yet, for illustrative purposes let's stick with that number.

    So, 42.5 million units at a licensing fee of $42.5 million. In the most recent full fiscal year Apple reported net earnings of $41.7 Billion. Therefore the $42.5 million expense amounts to slightly more than 4.75 hours of net earnings. Thus even in this exaggerated scenario Apple could pay to license all existing A1428 iPhone 5's from the morning bell to lunch in one day.

    Back to the beginning: this further underscores my entire premise that for Apple this is a middle finger to customers. There is no great financial or technical hurdle to warrant the lack of support for AWS UMTS on existing A1428 handsets. None.
  • mveras1972 - Sunday, April 28, 2013 - link

    I think you are all confusing yourselves with these rumors. I don't believe any of these rumors about licensing by Apple, etc. I don't believe there is any such "new A1428". The so called "new" iPhone 5 is simply the same iPhone 5 with carrier update T-Mobile 14.1 which is being sent over the air to T-Mobile iPhone 5 users to enable AWS on iPhone 5 phones old and new. You must be on iOS 6.1 or later to receive the update. This is NOT an iOS update so that's why Apple says it cannot be updated that way. It is T-Mobile's update, not an Apple update. They have nothing to do with this. So yes, you can take your unlocked AT&T iPhone 5, hook it up with a T-Mobile nanoSIM and let it get the OTA carrier update. If the Carrier field of your iPhone 5 says T-Mobile 14.1, then you have AWS bands enabled to enjoy 3G and 4G data.
  • Mr.Haswell - Friday, March 29, 2013 - link

    Would a ipcc update kill a jailbroken iPhone?
  • bearxor - Sunday, March 31, 2013 - link

    I'm pretty much just expecting a modem firmware flash from the new model on to existing A1428 devices.

    It's irritating, but at least I'm currently jailbroke and in a position to do something like that.
  • Mr.Haswell - Sunday, March 31, 2013 - link

    Now since it's just a ipcc file update, could someone theoretically extra the file from a T-Mobile iPhone then upload it to the internet? One might have to jailbreak their iPhone to install the file, but it's a small price to pay if Apple doesn't release an update.
  • bearxor - Tuesday, April 2, 2013 - link

    It's likely not a carrier bundle update. There's already a hacked carrier bundle that will activate LTE. The modem baseband is going to have to be flashed.

    Hopefully someone can extract that from the iOS update that will be released on April 12th (or the ipsw for the new version of the iPhone) and make an installer to patch it to older A1428 devices.

    There was something similar done with the iPad modem firmware being put on iPhone 3G's so they would be unlockable so I'm optimistic something can be done to get current A1428 units on AWS HSPA+.

    Now, how long it might take is a different story.
  • makabe - Wednesday, April 3, 2013 - link

    Really good explanations--I'm not thinking of selling my unlocked 64GB iphone 5 anymore. Looking forward to the modem firmware update...
  • bearxor - Friday, April 5, 2013 - link

    There's no guarantee. I'm just very optimistic.
  • Shadowmaster625 - Tuesday, April 2, 2013 - link

    Why is there no blackberry Z-10 review? I consider this an epic fail for what I thought was a respectable tech site.

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