I'm using a smartphone.
When I turn off the cellular data or my mobile phone, I can still call and send SMS. Does that mean in this case the mobile using GSM? How can I know if it is GSM or GPRS? And which technique is used TDMA or CDMA?
When I turn on the cellular data I see for examle 3G or 4G or LTE active. In this case, does that mean GSM or GPRS is inactive and voice and SMS is also sent via 3G or GSM is separately always active?