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I'm not sure how to describe what I'm looking for. I'm working on Linux.

I have a remote device with a 4G SIM card which I need to connect to by dialing in and then running some commands over the resulting serial connection. However, I don't have a local modem to do the testing, and it looks like all the mobile phones I have access to cannot work as modems (perhaps I'm not doing it correctly; I'm using the usbserial module and I don't see any /dev/ttyUSB* or /dev/ttyACM* device appear).

Is there some service (public, paid or otherwise) that would allow me to create a virtual serial device over which I could place calls to the 4G network?

Edit: ok, perhaps it's not 4G (I'm not sure about the exact network it uses), but it's definitely something one dials into.

John Smith
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  • Can you specify when the remote device is? I don’t think you can “dial in” to a 4G modem, that would be more something that was done way back in 2G (oh CSD, HSCSD, I don’t miss you!). It is more likely you just connect to it over the Internet, though many (most?) mobile networks use some form of CGNAT so you can’t usually connect to the device, it’s usually more the other way around. Details will depend hugely on the exact device. – jcaron Mar 26 '21 at 13:15
  • Yes, the manufacturer says I have to dial in. And indeed if I call the number with my mobile phone I can hear the classical modem beeps and buzzes upon answer. More info: after some research, although the manufacturer doesn't state it clearly, I think the device speaks some form of IEC 62056-21 protocol. – John Smith Mar 26 '21 at 13:39
  • This seems to be specific enough that you probably need a device designed for this, this is not run-of-the-mill 4G. And if it does indeed use actual modem-like modulation, then it's probably by far the least efficient way of using 4G! Also given that it's actually impossible to get a POTS landline in many places nowadays, this is not quite future-proof. Mobile phones will do packet data, so when they act like a "modem", they really are routers. I'm not aware of any option to use a smartphone to emulate a modem or of public dial-out modems... – jcaron Mar 26 '21 at 15:53
  • Possibly related: https://superuser.com/questions/748154/use-a-smartphone-as-a-dial-up-modem – jcaron Mar 26 '21 at 15:54
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    Do you have a POTS line? I.e. a regular, old-style telephone landline, not through a VoIP box? If so just buy a modem. Surprisingly given how quaint and "specialty" they must be nowadays, they are still quite cheap. – jcaron Mar 26 '21 at 16:46
  • I agree with @jcaron. To me, this appears like an old device. I'd be curious to know when it was manufactured.
    On a lighter note, be careful what you call into. These kids started a lot of trouble -
    https://www.youtube.com/watch?v=KXzNo0vR_dU
    BTW, admins, is such humor permitted on this board or does it always have to be serious ?     – kalyanswaroop Mar 26 '21 at 18:50
  • @kalyanswaroop ahah, I knew it had to be Wargames even before I clicked on the link! – jcaron Mar 26 '21 at 23:08

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