VoLTE support progress

I like to preserve CSFB compatibility support for 2G here in Europe, but for those (still) using 3G (WCDMA) within Asia Pacific and Latin America (adopting the APT700 band plan) regions/countries, like you @irvinewade or @BarryK, and looking forward to use VoLTE on their Librem 5 might take a look at SIM7912G-M2 (MDM9240, S2-1085D, Cat.12, M.2 card, Global) as it should be RCM approved (or will be soon).

For the rest of us (including average joe under FCC umbrella) might be that Purism is the only one to provide some update on M.2 card(s) that will be provided or not. Therefore my question here: why or why not to consider usage of THALES DIS AIS Deutschland GmbH Cinterion PLS83-W (GCF Reference: 9540) module (LTE Cat.4 with 2G/3G Fallback)?

Also, MDM9607-0 (LTE Cat.4) supports VoLTE (like within SIM7600G-H R2 module, for example) so expecting that the BM818 M.2 modem variants will do the same is not something to dismiss, but not to forget that:


For additional info, my Red Pocket (AT&T) SIM had already been activated in another phone, so all I had to do was insert it into the L5 to have full functionality. So I suppose you could say that “AT&T allowed” it; there was no approval process for the L5 specifically, though.

Almost certainly. If you pop in the appropriate SIM.

Three. As noted before, I’m now using the Truphone prepaid SIM, which runs on AT&T in the U.S. (as well as major foreign networks when traveling abroad).

Assuming T-Mobile hasn’t shut down 3G yet, his situation could change suddenly when they start refarming. In the last 2 locations I have lived (I moved over the summer), I had problems with incoming and outgoing calls with a T-Mobile reseller (which was also Red Pocket service). [Clarification: That was with my Android.] It turns out that it was because the 3G signal was weak (or possibly degraded?), even though T-mobile had not shut down 3G totally at the time. That Reddit user may actually have issues without knowing it yet. I didn’t realize it at first, until I found out people had called me and not reached me, and then when I tested by watching my phone. (I saw a drop to 3G happen, but not a peep from my phone.) And when the Reddit user happens to move around in non-3G or weak-3G areas, he could find himself without call connectivity…maybe without even realizing it.

Just a guess, but he must have attempted to check the IMEI, and it was rejected. This is no surprise, since no network will recognize this modem, most likely. It’s an unknown device to them. I wonder if he just popped in an already-activated T-Mobile SIM or actually got them to activate it for him…?

(re AT&T) In my opinion, yes.

Surely impossible. Purism would have to construct their own nationwide network, build towers, buy spectrum, etc. AweSim is an MVNO service.

Almost certainly true. With the caveat that “allow” may entail using a SIM that’s already activated in another phone, at least until the L5’s modem starts getting recognized by the carrier as compatible.

(re T-Mobile) Their public statements about the “small” number of affected customers seem to gloss over all their customers with unlocked (non-T-Mobile-branded) phones, but we’ll see.

Agreed, although I believe they’ve said they’re investigating that now.


Correction: Page Plus is a Verizon reseller, not AT&T.

For general interest, here is a list of current AT&T MVNOs (excluding international SIMs like Truphone, I believe):

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Thanks, amarok. I meant to say that the wiki list only shows L5 users with voice-text-data so far on only two AT&T MVNOs: Truphone and Red Pocket (both yourself!)

So, that list so far shows L5 voice-text-data success on AT&T, Truphone (AT&T), Red Pocket (AT&T), and T-Mobile. But not Page Plus (Verizon) or Ting (T-Mobile). And, I’m skeptical of whether the user who got on T-Mobile in December is still getting on since 01/01/21.

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I added a 2G wrist watch phone to Mint Mobile (a T Mobile MVNO) just a month ago or so ago. It works fine now. When I activated the SIM card, the customer service person asked what the IMEI number is and I told him I just wanted to activate the SIM card for now and didn’t have the IMEI number on me at the time. He said okay and activated the SIM. When I was completing the activation from my PC, they sent me a code via text message to the watch itself. I typed it in online and then everything just works now. I was shocked when the text came in to the watch since I hadn’t set anything up on the watch yet, other than inserting the SIM in to it. The customer service person probably doesn’t care most of the time. If they refuse to activate your SIM, just call back in a few minutes and try with a different customer service person.


If T-Mobile stopped allowing non-VoLTE phones on its network in January 2021, then we should have seen a ton of angry comments on the internet about it. The lack of a public outcry indicates that T-Mobile is still allowing non-VoLTE phones on its network. It is clear that T-Mobile wants people using its network to upgrade to VoLTE phones, but it isn’t clear when it will stop allowing non-VoLTE phones on its network and whether it will have a strict whitelist of allowed phones or not.

I believe that T-Mobile is putting out these statements so that it has something to tell irate customers when it shuts down a 3G network in their area, but the shutdown of 3G will be piecemeal and T-Mobile doesn’t want to deal with the huge customer backlash of not allowing any non-VoLTE phones on its network. It would overwhelm its support staff and cause T-Mobile to lose a lot of customers to AT&T. Instead, T-Mobile drops scary announcements to get its customers to change their phones, but considering that T-Mobile only announced its change 7 months ago, I don’t think January 2021 is the real cut-off date for non-VoLTE phones. Since T-Mobile isn’t clear with the public about its VoLTE policy, I don’t think that Purism can tell you what T-Mobile is planning.

From @mladen’s email to you, we know that the spec sheet for the BM818 now says that it has VoLTE support, but it doesn’t sound like the MB818’s VoLTE is configured for specific carriers, so Purism is going to have to add software that configures for the carriers. That is how I interpret Mladen’s email, but I would appreciate an official statement from Purism to confirm that.

As for testing other cellular modems which @mladen also mentioned, it doesn’t look like Thales is offering Linux drivers for the Cinterion PLS83-W, so that one seems to be out of the question.

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Also just to add, but the T-Mobile news about dropping support was leaked to the press early - during a pandemic where they’re looking to still turn a profit is a bad time to not be able to control the narrative.

Id’d not be surprised if this stops being a goal for them for a little while longer, while they continue to refarm existing spectrum without risking any sort of official action until it can be seen as more politically correct to do so.

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The fact remains, though, that if you’re on T-Mobile or a T-Mobile MVNO, and the 3G signal where you live, work, move around, or travel is either very weak or non-existent, and you’re using a non-VoLTE phone, then your incoming and outgoing calls will probably not connect. Your phone will likely not even ring (in or out) as it drops to 3G and looks for the signal. That’s what was happening with my Android on T-Mobile MVNOs…and I didn’t even realize it for weeks.

Calls didn’t go to my voicemail, either.


Wouldn’t all the VoLTE fooforah be moot if AweSIM included a libre service that worked like Google Voice? :kissing_closed_eyes:

Speaking of that, and somewhat related, I tried to install Linphone on the L5 a while back, but it didn’t work out so well. Maybe with Byzantium…

Look at Mycroft AI

For what it’s worth, I have been testing out VoLTE over T-Mobile networks by enabling the VoLTE mode on the Librem 5 modem (which is disabled by default right now). Once enabled, I can successfully receive calls over 4G.

Unfortunately when I attempt to place calls, the carrier disconnects them, sometimes after the other side rings, sometimes before. When in this mode I have to go into modem settings and tell it to be 3G only and then I can place an outgoing call.

This leads me to believe that it could simply be a matter of having the carrier add the modem to the allow list for VoLTE. Or at least that’s the next step we are pursuing. We’ll know a lot more once we get past that point and can test outgoing VoLTE calls once the carrier allows them.


Nice! Making progress.
Thanks for the update, Kyle!

Not having read the whole upper part in detail, one question:
Which modem? Thales or Broadmobi?
I thougth first one is not available for Evergreen while the latter does not support VoLTE.
That’s why I am confused.

This is with the Broadmobi BM818-A1 modem that we ship in all North American phones. If you look up the specs for that modem you’ll see that it does claim support for VoLTE and indeed includes a toggle for it with an AT command, there just hasn’t been extensive testing of it, or adding it to allow-lists throughout global carriers yet.


@Skalman originally posted links to a Broadmobi BM818-A1 spec sheet and manual in a different thread: Librem 5 BroadMobi modem reports wrong (?) manufacturer/model info -- bug in firmware? Where to find documentation for the modem?

Specs are at: https://p.globalsources.com/IMAGES/PDT/SPEC/593/K1172549593.pdf


Kyle, thanks for providing some Purism voice on this issue, which sounds quite encouraging. To clarify, are you suggesting that enabling VoLTE on the BM818-A1 is possibly just a matter of establishing permissions for Purism to use this particular modem on a given provider network? Can you offer a short task description and timeline for getting a given modem added to a given allow list? (What is that and how long does it take?) Is Purism pursuing both T-Mobile and AT&T allow lists for the BM181-A1?

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I’m no expert in VoLTE or cellular modems, so I’m just giving my non-expert assessment based on my personal experience with trying this, along with my general expertise in troubleshooting things. Based on that, it seems the hardware does support VoLTE as it states, and works just fine for incoming calls, and that we just need to figure out why outgoing calls don’t work. It could be as simple as adding to the allow list, maybe once we do something else will come up. We’ll find out soon enough.

I really don’t want to map out a project plan, timelines, deliverables, etc. in this thread. I’m trying to participate in the forum as much as time allows, and can answer quick questions, but I can’t budget the time to research with the team and create GANNT charts, project plans, or other things like that.


We have confirmation from a member of the community that after performing the steps to enable VoLTE on their modem and rebooting a few times, they were able to make and receive VoLTE calls through their provider (1&1 in Germany).

So I’m even more confident this is just a case of getting carriers to allow it.


Thanks for looking into this! I am kinda curious how hard it is to “Get the carriers to allow it”. But sounds like we’re about to find out.

Random thought: Do carriers see this phone as just a BM818 A1, or do they see it as a librem 5 for their allowance checks? Mainly curious to know what they see and how.

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