Choosing the Modem

Sorry, I had already looked at that and I looked at it again. It doesn’t seem to answer the question. Is anyone connecting to AT&T using VOLTE and if so, using which modem?


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I’m using an AT&T MVNO (i.e. reseller of AT&T service) with the BM818-A1, which does not have VoLTE capability yet. Hopefully, a software/firmware update can eventually fix that, but it’s not certain.

I’m not sure the PLS8-US is available for purchase from Purism yet, but you can email Support and ask them.

I received an e-mail from Mladen Pejakovic, Support Manager at Purism, on 01/30/21 with the following answers to my two questions, confirming that the Librem 5 Evergreen may not be ordered with the PLS8-US modem at this point, and the reason is that it’s not sourced, available, and priced yet.

  1. Can the Librem 5 Evergreen actually be ordered with the PLS8-US modem? If so, then how is this done?

Sadly no, not yet at least.

  1. Is there actually an additional charge for ordering a Librem 5 with the PLS8-US modem? If so, then how much is it?

Yes, but since we do not have PLS8 modems sourced and available yet, the price hasn’t set yet.


This is an excellent question that no content on the Purism website and FAQ, the Forum, or the Wiki seems to be answering clearly. The only confirmation that I’ve seen in this Forum or the Wiki FAQ is that Librem 5 owners with the BM818-A1 modem (phone batch version unclear) have been been able to place 3G calls on the AT&T network. Also, as Amarok points out, the BM818-A1 is not capable yet of supporting VoLTE on the Librem 5.

I received an email from Mladen Pejakovic, Support Manager at Purism, on 01/31/21 confirming the following when I pressed Support about my concern that T-Mobile has announced that they are no longer allowing non-VoLTE phones on their network as of 01/2021, and AT&T has announced that they will no longer allow non-VoLTE phones on their network starting 02/2022. This explains why nobody has confirmed in the Forum or Wiki FAQ that they are using a Librem 5 to make calls on the T-Mobile network, and why Librem 5 users are still able to make calls on the AT&T network, at least using 3G. Mladen wrote, numbering his responses to certain questions of mine:

  1. BM818 modems support VoLTE (you can find its spec sheet online to confirm).

  2. We are in process of developing software to enable VoLTE on Librem phone.

  3. We will also consider other modems for use with Librem 5 in the upcoming months.

So, Purism is working to get the BM818-A1 to support VoLTE. In the meantime, I assume that the AT&T network is now the only network in the U.S. that will accept a Librem 5 for calling, and the clock on that functionality is ticking down till 02/2022. In addition, Purism is working on alternatives to the BM818-A1. Mladen apparently either meant the PLS8-US or possibly other alternative modems.


I asked Mladen Pejakovic, Support Manager at Purism, about an alternative spec sheet for the BM818-A1 modem, since the only one I could locate online at the BroadMobi website does not include VoLTE on the “enhanced features” list, as many posters on this Forum have pointed out, and various content on the Forum and Wiki FAQ has declared that the BM818-A1 “does not support VoLTE”.

In response, Mladen sent me a PDF of a spec sheet brochure for the BM818-A1 on 02/01/21, though he didn’t provide a link or cite the source, though presumably it was sent from BroadMobi. This Forum won’t allow the upload of PDF files. But, copy & pasted from the brochure, which seems to include support for VoLTE:

General Features
• Variant:
TDD-LTE B41(200M)
• 3GPP Rel. 10
• Supply voltage range: 3.3V~ 4.2V
• Operation temperature: -40℃ to +85℃
• Dimension:
• Weight: 6.5g
• M.2
• Voice
Speech codec(HR,FR,EFR,AMR,AMR-WB)
Echo Cancellation, Noise Reduction
VoLTE, Digital Audio and VoLTE
Point-to-Point MO and MT
SMS cell Broadcast
Text and PDU Mode
• Control Via AT Commands

Software Feature
• USB Driver for Windows 7/8/10, Linux
• PC Suite for Windows OS
• NDIS Driver for Linux
• ECM Driver for Linux
• Gobinet Driver for Linux
• RIL supporting for Android
• Protocols

Enhanced Features
• DoubleProtect-backup for Software and APP
• Temperature Management;
• GNSS: GPS,GLONASS,BeiDou,Galileo;


  • Uplink up to 50Mbps,
  • Downlink up to 150Mbps
    • HSPA+
  • Uplink up to 5.76 Mbps,
  • Downlink up to 42 Mbps
    • UMTS
  • Uplink/Downlink up to 384Kbps
    • CDMA 1x EV-DO
  • Max. 14.7Mbps(DL), Max. 5.4Mbps(UL)
    • EDGE
  • Max. 236.8Kbps(DL),Max. 236.8Kbps(UL)
    • GPRS
  • Max. 85.6Kbps(DL), Max. 85.6Kbps(UL)

Shanghai BroadMobi Communication Technology Co., Ltd Http://
Floor15, Building9, No.99, Tianzhou Rd, Shanghai, P.R.China
Tel:+86-21-60913308 Fax: +86-21-60913308-818


The USA edition Librem 5 has a PLS8-US modem.

Right, the Librem 5 USA comes with the PLS8-US Modem because Purism is building that modem onto the board themselves as has been described in the Wiki FAQ, but the regular Librem 5 may only be ordered at this time with one of the three variants of the BM818 modem.

By the way, I just found a link to that BM818 modem PDF brochure spec sheet that I referenced above e-mailed to me by Purism Support. Someone inserted it into a new post on the Forum that just went up a couple hours ago.

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So will the regular L 5 ever be available with the PLS8-US? I thought when they sent you the email where you picked your choice of modem it was supposed to be available then. The modem choices are still listed on the sales page. Confusing to me

I have updated the community wiki with this new information:

It appears that VoLTE support was recently added to the BM818’s spec sheet, but @dos has said in the past that the BM818 didn’t have carrier-specific profiles for VoLTE, so maybe this is why @mladen is saying that software will have to be added to the Librem 5 to make VoLTE work.

At any rate, this is good news that Purism is now working on adding VoLTE support for the BM818.


Yeah, I gave Mladen feedback that content on various parts of the Purism website is internally inconsistent regarding modem choice and he said he would pass that to the Marketing crew.

The answer seems to be, “We can’t say just yet.”

I thought the same as you did and was about to order a Librem 5 Evergreen when I realized that the drop down menu did not include the PLS8-US modem choice. I wanted that one because it “has VoLTE” whereas the BM818-A1 apparently “doesn’t have VoLTE.” Now it looks like both modems do, in fact, “have VoLTE”, but that either BroadMobi or Thale firmware development, respectively, and/or Purism software development is required to enable it on either one of them.

So far, I’ve seen no claim that anyone is actually using a Librem 5 USA with the PLS8-US modem for voice calling at this point, much less making 4G calls on it using VoLTE. I suspect that the PLS8-US will, in fact, not do so when tested. Also, I’ve seen no claim that anyone is using a Librem 5 with the BM818-A1 modem yet for voice calling with other then 3G on other than the AT&T network. As of 01/2021, I suspect that both the Librem 5 and the Librem 5 USA are each now usable for voice calling on only the AT&T network, and will only be able to do so until 02/2022. That is, unless firmware and/or software is implemented to support VoLTE on the BM818-A1, or on the PLS8-US for use in the regular Librem 5, if they can source a reliable supply.

That said, I’m slowly drifting toward the conclusion to just order the Librem 5, get in the queue, plan on a carrier that uses only the AT&T network so that I can use the phone for calling before 02/2022, and then take it on faith that Purism will have a vendor/firmware and/or Purism software fix in place before calling goes dead for non-VoLTE phones on the AT&T network next February.

I’ve just had confirmation that PLS8 modems are still not available from Purism yet. (I didn’t notice people had already asked about that recently, or I might not have bothered asking again.)

Edit: I didn’t look closely enough at the product I describe below. Words deleted and inserted to avoid being misleading.

I just noticed that Thales (which bought Gemalto) is selling a product called mPLS8 (-E or -US), which is a PLS8 in m.2 mPCIe form factor. Thales’ website claims this m.2 version is data only (no voice support), which would make it unsuitable for voice calls. However, they also have a PDF data sheet which says it has multiple operator VoLTE support and CSFB (traditional voice calls), so one of those pieces of information must be false.

PresumablyClearly Purism has not been proposing to use mPLS8 cards, but rather to assemble their own cards using PLS8 BGA modules, although I don’t know whether the mPLS8 existed when they decided to do that.

mPLS8 cards are available in 1 off quantity from Digikey, if some brave soul wants to try one, without any guarantees that it will work correctly! but nobody should buy one to put in a Librem 5, because it won’t fit!

Digikey has the same PDF data sheet claiming VoLTE and CSFB support. They also have an EDA/CAD model showing PCM1 pins on the m.2mini PCI Express connector, which would imply voice support, but they also show a pin for LED_WLAN, which doesn’t really make sense for a cellular modem (there is a separate pin for LED_WWAN) so I think it might just be a generic m.2mPCIe pinout, with not all pins necessarily being functional for that particular card.


It’s mPCI-E, not m.2, perhaps you confused with m2m which stands for machine-to-machine and means data-only. So datasheet is misleading, if you look on HID doc it clearly mentions audio pins as NC (reserved for future use)


Oh, so it is. Whoops!

I think I saw “m” in the part number (mPLS8) and saw from the pictures that it was in a mini card form factor and it never crossed my mind that people would still be using the mini PCI Express form factor for things like this, but it makes good sense when you consider the market it’s aimed at. (For example, you can still buy industrial SBCs with mini PCI Express slots.)

Gonna have to edit my post I think.

I just saw that Thales now has this modem available on m.2 USB: MV31-W. Although it’s a 5G modem (and the Librem 5 cannot use 5G) it has 4G and 3G fallback.

According to its datasheet, it is supported on many MVNO’s including AT&T, Verizon, T-Mobile / Sprint. It also has a broad range of LTE bands supported and boasts a (self-proclaimed) compatibility for worldwide networks. It doesn’t say whether VoLTE is supported or not.

Lastly, it supports Dual SIM with an embedded eSIM. I don’t really know what that means but I know some people have requested support for Dual SIMs.

It says it has a Linux driver, but I doubt it’s open source. Who knows though, maybe it might just work in a Librem 5 someday? However, it seems very pricey.

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The “details” page says: Voice support : Data only
(Still, if it works well for data then maybe it could be used in the Librem 5 handling all calls via the Internet connection somehow?)

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Dang. I guess it was too good to be true afterall. Thanks for verifying!