[cctalk] Re: Cell phone as a dial up modem.

On Wed, Aug 10, 2022 at 11:53:34PM -0600, Grant Taylor via cctalk wrote: I did it routinely in the late 1990s and early 2000s. I stopped once I got a GPRS-capable handset, since that was much cheaper to run: 1MB of data cost the same as a one minute call (which could shift 144kB at best, although 30-40kB was more typical) on Vodafone UK in the late 2000s. By coincidence, this is still the case for me now on Lebara NL, but the prices are *much* lower. My phone used a relatively obscure corner of the GSM standard known as CSD (Circuit Switched Data) which was essentially implemented as a flag set by the handset to tell the base station that it should use a dialup modem codec instead of the GSM voice codec for this call. CSD would only use a single GSM timeslot and was limited to 9600 bps, but HSCSD (High Speed Circuit Switched Data) could use multiple slots and telcos usually charged a lot more for such calls. So far, so good and It Just Works(TM), right? Unfortunately, there are confounding factors: * I suspect you're in the USA, which used NIH instead of GSM, and what it supported and still supports is any guess. * While GSM networks still exist, they've been pared down somewhat to make space for 4G and coverage can be patchy or suffer from congestion. 4G has *no* native support for phone calls: handsets either fall back to GSM (like my "new" iPhone SE which I had to buy after KPN turned off its 3G network) or 3G, or tunnel voice calls over VoIP. * Wikipedia also notes that "After 2010 many telecommunication carriers dropped support for CSD, and CSD has been superseded by GPRS and EDGE (E-GPRS)." Except of course that GPRS and EDGE are packet-switched services and no call is made, so it is not a direct substitute. * Modern handsets may not give you sufficient access to the cellular modem's serial port to send the appropriate AT commands to configure and make a (HS)CSD call. On the upside, 2G is mainly being kept around for the benefit of millions of embedded devices which have 2G modems, so I suspect CSD is still supported by extant 2G networks despite Wikipedia's claim to the contrary. I have not tested this hypothesis. So, just come to Europe and use an embedded GSM module instead of a whole phone :)