Hello.
I have similar issues as you have, mostly with DTMF tones not working properly with certain services (problem #1).
I do have issues with certain numbers that hang up instantly when I call them, like my bank. I guess this is because the Librem 5 is an unapproved device that I need to call in and whitelist with the services that blocks it.
Back to problem #1 though. Certain services handles the dialpad presses like they should, other services just registers everything as the number one and most services don’t register anything at all and hangs up after a while since there’s no option delivered to them.
I wonder what to do about this. If I should call these services and troubleshoot with them because to me it seems logical that a phone like the Librem 5 ought to support DTMF tones out of the box.
Edit: I live in Sweden and use a Swedish operator called Telenor.
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No bank, and no recipient of a call from you can know which device you are using to make the call (except for your mobile carrier, and they see that anyway because it’s how they know your device is authorized to be on their network, courtesy of the SIM). If there’s a problem with call rejection, it would more likely be based on a rejected phone number (VOIP, for instance, or perhaps your Caller ID registers as anonymous or unknown and the entity has a policy of rejecting those). For your situation, maybe you don’t have VoLTE enabled, so the call fails?
EDIT: Well, I suppose it’s not impossible that a spy/police/hacker group with specialized equipment might be able to collate data from various interceptions and sources to deduce or identify your device make, but probably not a bank.
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That would be my expectation. We would be talking about significant privacy fail. At least, if your statement is incorrect then I would like to know about it! 
Yes, it is possible that rejection occurs by the called party on the basis of the phone number of the calling party but that is a bit crappy as a primary security measure e.g. lost or stolen phone bypasses that straight away.
It is also possible that this is some kind of niche calling incompatibility scenario with the carrier i.e. works most of the time but sometimes fails, and it is the carrier dropping the call (or the phone).
I wonder whether it is possible to fingerprint DTMF. That is to say, I don’t know what the tolerances are in the DTMF specification but is there enough variation in e.g. frequency or duration to fingerprint? It also however depends on whether DTMF is transmitted in-band i.e. as actual tones then compressed by the codec or DTMF is transmitted out-of-band. (Or, following that thought further down the rabbithole, is there enough variation to use DTMF as a covert channel e.g. to send the IMEI? )
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I’ve been looking into this. It seems that in-band DTMF doesn’t work very well with more aggressive compression in the codec, such as may occur with the mobile network. (Maybe it would work better when you get to VoLTE, which permits HD audio, but only of course if actually using HD audio.) The mobile network protocols support out-of-band DTMF. However that will only work if all parties in the chain (starting with the application software on the phone, then the firmware in the modem, then your mobile network operator, …) implement it correctly.
I note that some modems have, apparently proprietary, AT commands that allow tweaking and messing around with this functionality. (However a typical user may not have an IVR at the other end where it is safe to send random crap and a typical user may not be able to put a frequency analyzer on the other end of the call. I am a typical user. I have not tested these AT commands.)
As a digression, the situation is more complicated with VoIP - because with VoIP there are (at least) 4 settings for how DTMF is handled and the setting chosen may have to be negotiated in the protocol and, as above, for it to work it has to be correctly implemented all the way along the chain. The basic 4 ways are: in-band, RFC2833 superseded by RFC 4733 (basically DTMF over RTP), SIP INFO (RFC 6086), and “automatic” (i.e. try to find something that works). I note that my VoIP box actually offers 6 choices but typically with little documentation as to what each choice does.
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I have a hard time following all of the technicalities here. I have “4G” displayed next to the bars. My Liberty Phone is a month old.
Should I install bm818-tools and enable VoLTE?
Regarding the bank, I have called with a hidden number before and no problem. Maybe you don’t mean the phone number though. What should I ask from them to do for me?
Thanks!
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Yes, if your carrier requires it or recommends it, and especially if there is no 3G or 2G left in your area. Remember to reboot after enabling it.
I did, but it was just a possible reason.
I would first see if VoLTE improves the situation. I don’t think there’s anything your bank could specifically do, unless they have some kind of fault in their phone answering/routing setup. In that case, they would need to fix it themselves.
According to https://www.korewireless.com/network-sunsets/ projected shutdown of 2G and 3G for Telenor Sweden:
| Country |
Operator |
Date |
Service |
| Sweden |
Telenor Sweden |
12/31/2025 - Provisional planning |
2G |
| Sweden |
Telenor Sweden |
12/31/2025 - Provisional planning |
2G |
| Sweden |
Telenor Sweden |
12/31/2025 |
3G |
| Sweden |
Telenor Sweden |
12/31/2025 |
3G |
It’s possible changes to network coverage have already started in some areas, of course, and the above dates may or may not be accurate. I would just check with Telenor to find out the current status of coverage in your area.
That’s for data/internet; it’s irrelevant unless it remains there during a call, which is what you want (i.e. Voice over LTE/4G).
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That’s what I would suggest as a starting point. Can the OP confirm by testing that 3G calling works in his area? (That is: phone is showing 4G, commence a call, phone drops down to 3G, call works, when call ends phone goes back up to 4G.)
If the OP has not already enabled VoLTE then I would have to assume that 3G calling is working just fine (otherwise all calls should be failing and the OP would have noticed this).
If 3G calling is working just fine, based on the published schedule, enabling VoLTE should still be on the OP’s radar for some time this year but it may actually be unhelpful to enable it now.
I say this in the sense of … it’s a potentially unrelated change without theoretical justification and is just moving the goal posts and potentially introducing other variables.
The opposite perspective is … we don’t know what is causing the problem with DTMF so we might as well try something (as long as the OP knows how to back out i.e. disable VoLTE if things get worse not better).
I went looking to see whether there are any notable implementation differences between out-of-band DTMF over 3G and out-of-band DTMF over 4G, but didn’t find anything.
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When I make a call the “4G” just stays “4G”, it doesn’t drop to 3G. I’ll try the bm818-tools soon and let you know how that experiment goes.
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