iPhone can support VoLTE


Earlier today, T-Mobile announced that it has pushed the button to launch its Voice over LTE service in Seattle. This means that Seattle-ites will be able to make regular voice calls using an LTE connection, and not have their phones switch to an older network technology to do so.

One slight caveat: Only specific phones will be able to make use of the service right away. T-Mobile stated that – after a software update – the Galaxy Note 3, LG G Flex and Galaxy Light would all be able to take advantage of VoLTE.

One question we’ve been asked after the announcement – and has come up elsewhere online today – is whether or not the iPhone will support this new service. And the answer is: Probably not.

But, the iPhone is technically capable. It just comes with a compromise. One of our regular followers, Joe, got in touch with us. Turns out the iPhone 5, 5s and 5c has some coding in it pointing towards VoLTE. The code is within the baseband itself, or the firmware of the actual chip Apple uses for LTE connections. Specifically, the Qualcomm MDM9615m, which is used in all of Apple’s LTE devices, including iPads.

Screen Shot 2014-05-22 at 23.24.29

As you can see, VoLTE is specifically mentioned within the iPhone chipset’s own firmware. So, the chip itself is capable of making calls over LTE. The reason it doesn’t do so right now is because Apple/T-Mobile haven’t released a carrier update to make it happen. And the sad news: It probably won’t.

Screen Shot 2014-05-22 at 23.27.59

A more in-depth look at T-Mobile’s carrier settings (above) reveals a string of code related to the way LTE can behave. This particular code string is found within the overrides PRI file. This file exists for every carrier, and tells the phone how to behave on the carrier in use.

For current LTE devices there are two kinds of calling methods. The one most often used, is the one displayed here. It uses VoCSFB, referred to here as “CS” or “Circuit Switched”.

Currently “CS Voice Only” would indicate that it’s forced to use the Circuit Switched domain. This tells your phone to use older network technologies for phone calls when you have an active LTE data connection. The rule ensures that if you receive a phone call while you’re using LTE to browse the web, or use data in any fashion, it’ll downgrade to 3G/HSPA+, to ensure that you can keep both connections running at once.


The carrier bundle could be altered to change this rule, so that voice calls could be made over an LTE connection, taking advantage of the chipset’s VoLTE capability. #winning

Uncertainty – Simultaneous Voice and Data with VoLTE?

Here’s where I get conflicting arguments chatting with our various network and bandwidth gurus. One believes a carrier update is all that’s required to get this service running on an iPhone. VoLTE and any other data connection should work just fine at the same time. In the same way that you can take a FaceTime audio call over LTE, or have background data or iMessage while browsing the web, you should be able to receive a VoLTE call browsing the web.

Internet data is packet switched domain as well. Wireless networks have two subsystems: a circuit-switched and packet-switched subsystem. The circuit-switched subsystem (called a domain by some) handles SMS and voice calls. The packet switched subsystem/domain handles the multi-media aspect of MMS (the message itself and signaling is handled by circuit-switched domain), and also handles IP data sessions (which is what VoLTE and internet data run on). LTE is special in that it lacks a circuit-switched domain to handle voice calls and SMS.”

Our second school of thought is that the LTE chip in the iPhone isn’t capable of running voice and data connections simultaneously. I say that, technically, VoLTE is a data connection, so in essence the iPhone can’t have a VoLTE call going and have you browsing/streaming at the same time.

Addressing the issue of the difference between FaceTime and VoLTE:

Because FaceTime is a service that isn’t hosted by the carrier and doesn’t occur in the carrier’s IMS Packet Switched domain, which only allows for carrier specific packet data like texts and picture messages. FaceTime simply uses pure internet data. It’s no different than having multiple web pages loading at once in the Safari web browser on the device. VoLTE is a carrier specific protocol hosted by the carrier and does occur in the IMS Packet Switch domain where texts and picture messages are also sent through.’

So if a carrier update was released to take advantage of the iPhone’s VoLTE compatibility, users would have to sacrifice simultaneous voice and data. You’d be browsing or streaming in glorious full-speed 4G, then receive a call, and the connection to your on-screen content would close to make way for the phone call.

Not bliss.

[Edit: It seems the general consensus – among those who know about these things – is that the iPhone should have no problem carrying a VoLTE call, and browsing/surfing/receiving other data at the same time.] 

But VoLTE is possible

Which ever of the two scenarios is correct in regards to simultaneous VoLTE and browsing/data, it doesn’t change the fact that VoLTE calls are technically possible.

There’s a case to argue that Apple could allow a carrier bundle to come equipped with a toggle switch within the Settings app to switch simultaneous voice and data on or off (if it’s necessary). All this would do is tell the phone to either use VoLTE for voice calls, or switch to the previously mentioned “CS Voice Only” command in the code and route any calls to the 3G network.

And then of course there’s battery life to consider. VoLTE is a more power hungry connection that the current CS (switch to 3G). And we all know the iPhone’s battery isn’t up there with the greatest.

Thanks, Joe/Neal.

[Updated: Added the edit above, and removed a couple of sentences from the end. I’m more than happy to admit my technical knowledge on these matters isn’t anywhere near the level of those who I’ve been talking to. I wanted to present an article purely to let concerned iPhone users know that their phones are capable of taking advantage of the new VoLTE service, also providing some insight in to any stumbling blocks.]

Tags: , , ,

  • Chris Hilbert

    I asked T-Mobile about Nexus 5 support. They said:


  • Verizonthunder

    Ahhh glad to see my argument was correct from tmonews Seattle VoLte post.

  • Cam Bunton

    Stayed up late for those last two… I’ll try and get your comments tomorrow. 3am is not a happy bed time. ;-)

  • Matt

    I’m losing patience with T-Mobile and may be forced to take my carrier unlocked phone to AT&T. The in-building coverage is poor and I keep feeling like the donkey lead by the carrot with the promises of better coverage and better services – I’m still waiting for it to happen except I hate paying 70.00 a month for unlimited LTE data when the coverage just isn’t there. I don’t even get 4G HSPA+ in my own home. My brother with AT&T gets 2 bars of LTE.

    • cruzz563

      You should genuinely switch, Matt. That’s the beauty of no contracts and unlocked phones. Go to at&t for a bit and then switch back to T-Mobile once coverage improves in your area if you feel at&t isn’t right for you. I would if I was in your situation. :)

    • Jay J. Blanco

      i hated the unlocked experience with tmobile so i got a branded tmobile phone so i can have wifi calling. it makes a big difference in a situation like your. T-Mobile wont have good in door coverage until after 600mhz auction. unless your in their 700mhz area.

    • FreydNot

      You should drop the unlimited data if you never get to use it.

    • Joe

      Just a suggestion, but have you given the T-Mobile carrier update hack a try? It does help with reception issues.

    • schweddyballs

      Your gonna be waiting longer buddy, get a tmo phone or go to ATT and stop crying.

    • Nate Opgenorth

      Its a shame T-Mobile doesn’t have low frequency spectrum, if they had an even decent amount of 850MHz spectrum they could refarm LTE or even HSPA into it like they are doing with 1900MHz. Heres to hoping with mergers they can eat up all the spectrum they can get.

  • dontsh00tmesanta

    Why enable when iPhone 6 will have it enabled

    • Anonymous

      Why support phones people currently use when it will be enabled in a phone that hasn’t been announced yet question mark.

      • dontsh00tmesanta

        Why enable it when the I6 will have it thus creating more sales

  • “A new chip that supports VoLTE and LTE data simultaneously”: There’s so much wrong with this statement that I don’t even know where to start.

    • mjoecups

      I agree, this whole article is a catastrophe of technical ignorance.

    • Joe

      Well, you can certainly lay down your thoughts and ideas in a rational manor. That’s why there’s a comments section. If you have a different view on the matter, let’s hear it. But can we do it without any rude comments? I’d like to have a good discussion where no one feels the need to take things personally and retaliate in a negative manor. :)

      • Joe

        Here’s my input, if I may. Utilizing VoLTE in a single chip, in theory, would require using different SIMs for the GSM/WCDMA and LTE radios, but comes with the obvious penalties of increased size, cost and power consumption (as is with voice + data over LTE) and, in addition, the cumbersome management of two subscriptions. Doing the same with one SIM card has been proposed, but such arrangement is not currently acknowledged by 3GPP standards, as this would lead to the registration of one SIM card to 2 core networks (2G/3G CS core and 4G EPS) simultaneously. Using dual radios would be ideal as it would overcome some of the limitations of VoCSFB, such as dropping any active LTE data session, call setup time, etc.

        • Nate Opgenorth

          Meanwhile UMTS networks haven’t had any trouble what so ever handling voice and data at the same time. Two SIM cards? Dude your making this WAYYYYY to complex, VoLTE should be able to handle data and voice without insane measures like dual radios or dual SIM cards, I doubt the 3GGP would fall on its sword with this when a technology released in 2002 was already doing this (UMTS). I blame Verizon for being stupid and not just using GSM from the start or better yet follow in Japan’s steps and skip GSM entirely and use UMTS and be lightyears ahead of everyone else. CDMA2000 is a bad joke, we have 4G phones that don’t just drop to 3G for calls but drop to 2G for calls (1xRTT)!

  • Ron S

    I’ve been able to initiate HD calls to tmobile users randomly for the past few months on VoLTE here in Newark California

    • Joe

      This is just an assumption, but I’d willing to bet that MetroPCS areas are already VoLTE capable. Neville Ray, CTO of T-Mobile, said during the merger that T-Mobile would continue to maintain Metro’s existing VoLTE services on it’s towers which are now also part of T-Mobile’s LTE network footprint. Since the LTE towers are shared between the 2 companies, VoLTE is active on them and VoLTE capable devices should be able to access them, no matter which carrier the device is coming from.

  • Ron S

    In my T-Mobile note 3

  • Ron S


  • milanyc

    This article is a bunch of mud stirring nonsense, without any strong opinion. Is iPhone capable of connecting to VoLTE and utilizing talk+surf at the same time?
    Well since the original poster never made that commitment, let me give you that answer.

    Yes it is.

    Qualcomm MDM9x15 baseband processor that’s inside iPhone 5S is fully VoLTE compliant, and talk and surf is an essential feature of that service since LTE Release 8. There aren’t any what’s and if’s. I have no idea what are you trying to argue here, exploring the “gray” area and not committing to yes or no answer.

    So there you have it, all that needed to be said out of that entire amateur hour nonsense.

  • randian

    If VoLTE is just a TCP/IP stream over LTE why can’t you simultaneously use voice and text just like you can have two apps simultaneously access the Internet?

  • Adrayven

    This sounds like a click-bait article.. err.. by definition, VoLTE stream is data.. soooooo… yeah..

    Joe.. you’ve made this into something it isn’t.. You seem to forget.. The Galaxy S4/S5 is not on the list either and those are fully capable.. and newer than the Note 3. The Simple reason is there are a LOT more iPhones and S4s and S5’s out there.. They didn’t want to overwhelm the network with a large volume and just started with the model of phones that had a lower volume of people to do testing..

    Please stop with the ‘click-bait’.. lets start a fight for the sake of the fight..

    You damn well know and expect the list to expand.. No one single phone has a larger customer base than those 3 models.. Those will likely be added last. I hate sensationalistic articles.. dumb reality show types.

    • Joe

      Topic: Whether iPhone can theoretically support VoLTE or not, and if so, where’s the proof? Proof has been provided, so it’s now up for debate (not arguing) whether VoLTE will cost voice + data abilities on the iPhone. We’re not talking about what all devices support it. That’s all in another article and off-topic for this article. The phones listed are simply a few examples of capable handsets. We don’t need to go down the entire list.

      Also, do you see my name as the author of the article? As much as I would like to satisfy you by fixing any problems you see, this isn’t my article nor is this my website. I have no control over what’s written and what isn’t. I simply contributed to some details specific to the iPhone and it’s VoLTE capabilities. Getting angry with me and cursing at me over something I can’t control is, not only unacceptable behavior, but also completely unfair of you to do.

      Also, the S4 came before the Note 3, but you are correct about the S5.

      S4 Release Date: Late April 2013
      Note 3 Release Date: Late September 2013

      • Michael Allen

        No,proof has not been provided. Evidence that suggests it MAY support it has been provided. Or more specifically,we don’t know that it works. Think of it this way,how much effort would they go to ,to fix a problem with something that was not being,and might never be used. Would they spend hundreds of man hours on it and delay the product launch. Or would they just send it out and not worry. It could be half finished. It could be broken. Or it could work just fine. Or it could be code left over from qualcom reference code they didn’t bother to strip out. But its somewhat likely that its there,and probably does work. But to say its been proven is a serious overstatement. Its not proven until someone makes a VOLTE call.

  • TmobileTee


    • HeatFan786

      Is that with the iPhone 5S?