Could the Librem 5 ever support "WiFi calling"? (UMA/GAN)

I find myself wondering if the Librem 5 will ever support WiFi calling, also known as “GAN” or “UMA” according to Wikipedia. Most new phones seem to support this.

For those who don’t know, WiFi calling essentially replaces the cellular radio link with a tunnel into your carrier’s network over WiFi and the Internet, in situations when you have WiFi but no or poor cellular coverage. You can use it to make and receive calls and to send and receive SMS and MMS messages, which are billed to your normal account using your normal number.

Does anyone have any idea about what it would take to support WiFi calling, and how likely or unlikely it is for the Librem 5 to ever support it? For example, does it require any binary blobs or non-disclosure agreements, or just open standards and access to the SIM? Does it require tight coupling between the WiFi, CPU and baseband, or can it be done with the Librem design? Has the Purism team looked into it at all?

I suppose it might be related, in terms of how it works, to VoLTE, which I guess prompts a different question about whether that will be possible to support.

Of course, the Librem 5 will be able to use Matrix for VoIP, but that covers slightly different use cases compared to WiFi calling.

For me, this is a “nice to have” rather than a necessity, but it is something that I would probably make use of, given the extent to which buildings often interfere with signals.


Matrix support VOIP, which can be used on WiFi. I fail to see the difference between Wi-Fi calling and VOIP.

“WiFi calling” is a term that’s used specifically to refer to a kind of VOIP that is provided by your cellular network provider (carrier). By definition, it connects to servers provided by the cellular network provider and authenticates using the SIM card in the phone.

Its primary benefit is seamlessly improved coverage for the conventional cellular service into all locations where the device has access to the Internet using WiFi, using the same telephone number and the same billing account, with no setup or configuration, and no need to load a separate application.

This contrasts with other VOIP services, which tend to have advantages such as low cost, privacy and flexibility, but cannot normally make direct use of a telephone number provided by your cellular network provider, and tend to operate as a separate service.

Of course, you can achieve functionality similar to WiFi calling by using a standalone VOIP service as your primary telephone service, but it requires a different arrangement of service providers. My question is specifically about WiFi calling.

I make no claim about which solution is best. I think both have valid use cases.


Further, WiFI calling (at least with the carriers I use) allows one to place calls that roam from WiFi to cell to WiFI and these calls are to the PSTN and the person on the other end neither knows nor cares that I’m using WiFi calling . . . so definitely not Matrix.


Since I have no cell signal from ANY carrier for about a mile radius right around my house I HAVE to have wifi calling ability. I have an AT&T femtocell now that works well when it’s up but it crashes fairly often anymore. So I’d really like to purchase a Librem 5 but won’t be able to unless it supports wifi calling.

As my current phone is dead I have to buy a new phone now. Do I buy a cheap one while I wait for a wifi calling enabled Librem 5 or do I buy a nice one since wifi calling won’t be supported on the Librem 5???

ANY help answering this question would be GREATLY appreicated!


I’m interested in this as well

I see that WiFi calling is also being called “VoWiFi”, to add to its existing profusion of names.

Skype would provide this if you pay for a Skype out number, etc. Not what the OP is after but a solution nonetheless.

yes, this needs carrier support, but there are a lot of carriers already supporting it:

In theory this could happen.
Voive-over-WiFi (VoWiFi) aka WiFi-Calling is an open standard and can be implemented as free software.

However, it is also a very complex standard that is very difficult to implement (as is VoLTE which is closely related and based on the same software stack).
I don’t see a free IMS/VoLTE/VoWiFi-stack for phones coming any time soon; if the Librem gets VoLTE, it will be a proprietary implementation in the blackbox modem, which right now is the only reasonable way to do it - since the WiFi-module is separated, it will not be possible to include this.

Additionally there is the issue of carrier certification: mobile network carriers have stringent quality requirements, and they tend to whitelist only certified implementations (which doesn’t necessarily exclude free software implementations), because they get blamed for poor voice performance (drops, noise, other issues).
This hurdle would have to be passed as well.

Again, I can see this happening, but not in the near future.
As it stands, there are no open implementations even for android which relies solely on proprietary baseband-firmware in combination with proprietary userspace support.


I really don’t know my low-level stuff very well, so this is a genuine question: Is there something more to VoIP that would require VoWifi to exist separately?

There are at least some open source implementations of VoIP, though whether they are any good is beyond me

I’m not sure I fully understand your question, but VoWiFi is a type of VoIP. VoIP is the general concept of conducting voice calls over an IP packet data network, and VoWiFI is an example of a specific VoIP standard. Other examples of VoIP standards or platforms include SIP, Matrix, Discord or Skype. Each requires a different implementation. Some are based around service providers that insist on non-free software. VoWiFi is the standard used by cellular carriers for seamless VoIP using your cell phone number. Its integration with the cellular network makes it more complicated to implement.

That was my suspicion. You seem knowledgeable enough to confirm it. It’s interesting that VoLTE may be easier to support than VoWiFI. Good post, thanks!

Well, VoIP is just a very generic term describing the transport of voice over a IP-based connection, it doesn’t necessarily describe specific technology.
It tends to be used most often for SIP-transmissions, which would include VoWiFi in a broader sense.

Where VoWiFi differs is the tight integration in the modern carrier-grade telephony system called IP Multimedia Subsystem, aka IMS.
IMS has a lot of extra complexity, and there are basically 2 reasons for that:

  1. Integration into Carrier-Networks (including legacy support)
  2. Overall Quality

VoWiFi is expected to be very reliable, which includes a lot of roaming scenarios, it will allow better location functinality for emergency services (when you call 911, 999, or 112 or whatever your country is using), and it has a tightly integrated Quality-of-Service functionality.

The classic example would simply be support for roaming between mobile networks and your home WiFi, in which case a traditional SIP call would drop, Skype and others will either drop or at least severely lag, and in a proper VoWiFi situation neither party would notice.

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Generally that is not actually the case, however, if the VoLTE implementation in a baseband is used and the application-processor uses separate WiFi hardware, VoLTE is indeed easier done, because you don’t have to care to implement it yourself, the baseband handles it and you just interchange PCM audio with between BB and AP.

In his interview with Bryan Lunduke back in August 2017, Todd Weaver stated that the Librem 5 can be used for Wi-FI calling. That discussion is at about 12:00 into the interview.

Wi-fi calling across the matrix client I would assume. Not wi-fi calling through a carrier service. When I saw this thread, I thought the same though: Why would I want to call over wi-fi through my carrier who will charge me to use this feature, when I can just use the wi-fi I’m already paying for to make VOIP calls using software that supports that?

I have strong preference of using VoWiFI rather than other VoIP types (Matrix, SIP, whatever) because of the following reasons:

  • my carrier plan has flat rates to landlines and to all other mobile carriers in my country
  • I’m living very close to the border (couple of hundred meters) and my carrier’s signal is really bad in my apartment. I’d really really benefit from VoWiFi because it would mean a better call quality and no dropping signals and/or calls. People could reach me without using an extra client or number. They’d just need one number from me and would always reach me on the same device.
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Too bad a Skype Out number is a no go for you, as that would fix your problem as well.

Skype Out doesn’t help people reaching me. And Skype In would mean a) interrupting calls when changing networks (mobile to wifi or vice versa) and b) eating away from my monthly data volume when not in a WiFi.

And Skype being proprietary is a show stopper anyways.

The fact is that the Librem 5 will be usable both with and without the facility to make calls via a cellular network. WiFi calling is a useful supplement to cellular calling. It’s a bit like having a femtocell in the building.

It would make no sense for me to use internet-based VoIP services for PSTN calls. I will already be paying for the ability to make and take calls via the cellular network, because that comes as standard with the most cost effective cellular data services. That includes the ability to use WiFi calling on supported handsets. Not only is the cellular voice call service effectively free of charge with my data connection (I can’t save any money by avoiding it), but it is also more robust to poor cellular signal conditions than VoIP over cellular data.

Given that I will already be subscribed to the ability to use WiFi calling whether i use it or not, being able to make use of it via a compatible handset will always be an advantage.

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