You're welcome.

Please do.
From what I have seen on-line, what you want to do is not and has not ever been a straightforward affaire, so your update will be useful to have. 

Indeed ...
I (and a great many here) can easily relate to that.

Best,

A.

It could well be.
The USB modem need to have the right firmware, matched to what services the telco offers through the SIM they sell you.

But, like I said, I've never used them.
You may need to check with the USB modem's OEM and also ask the telco issuing your SIM.

Again, cannot say.
I just found that bit of information and relayed it.

In my opinion, your best bet is to check with the telco/provider.
Sorry I cannot be of more help.

But please do let us know how you fared with this.
I'm sure it will be useful to someone further on.

Best,

A.

@aluma: So, it will not automatically do, whatever it does, thanks.
As for the screenshot, take a look: http://oscomp.hu/depot/opera12_mm_screenshot.png
It does not appearing in Opera 12. But it did work from Ungoogled Chromium. (But that is not my default browser.)

@Altoid: My brother just bought some USB modems from the net, not from the telcos; you say they also might block voice via the SIM?
If USB modems do not support phone calls en generique, then how can one make a GSM phone-call-center with Asterisk?

No.
My apologies for the confusion.  8^°

When I say "... only seen these once, long ago ... " I am referring to these type of modems.
ie: cellular network based USB modems using SIM chips as opposed to land line modems using copper.

My comment with respect to the 14.4 USR Sportster dial-up modem (a ca. 1994 a land line modem) was only to illustrate your present situation.
ie: the fact that the issues you are having seem to be the same ones I had over 30 years ago.
And how much many things have not changed.

Before purchasing another one of these modems, you may want to consider getting in touch with the telco that will actually provide the cellular phone service for you and ask them if they can provide voice service with a USB modem+SIM chip or not and and if so, if they offer one or can suggest a brand/model.

Bear in mind that different telcos may offer different services/options/rates.
eg: a telco may offer voice and (maybe) tethering with a cellphone/smartphone but only data (and not voice) with a USB modem.

Also bear in mind that different telcos may offer different services/options/rates.

If they do, get the brand/model/etc. and try to find out all you can about it before you purchase it.
Specifically any on-line reports/reviews that can give you some information on how to get it to work reliably under Linux.

Edit

Forgot to add this, cannot say how acccurate this information is:

Best,

A.

Should i instruct it to do something?

I have no idea.
Maybe start with this?
https://manpages.debian.org/experimenta … .1.en.html

Regards.

Regards.

@aluma: I've looked for "Daedalus", but i found no modem manager named like that. Did you mean Devuan 5.0 "Daedalus"? I was curious about the modem manager's name. Or is it "Modem Manager"?

BTW, do you guys know any kind of USB GSM modem which has voice support?

Regards.

I really could not say, I have only seen these once, long ago and on a friend's laptop, also with connectivity issues.

That said, a couple of the links I posted are from long ago and another from 2023.
So it would seem that that the problems you are having have been going on for the longest while but it also means that there may be more information out there.

I recall going through hell (ca. 1994) with a 14.4 USR Sportster dial-up modem and the undocumented AT commands I had to search for all over to get it to work properly, obviously not with today's web.

Not to mention the ridiculous amount of cash I had to pony up because of the endless amount of dropped dial-up calls caused (in this model) by a defective chip.

Best,

A.

@aluma: I use picocom. What is the name of that GUI-driven modem manager?