If my RC7620 (EE SIM) dials out on 4G to my O2 phone on 4G then I can use an external DTMF chip to generate DTMF tones into the RC7620 and I can hear these on my phone (although a little distorted).
However, if I press the numeric keys on my phone to generate DTMF tones in the other direction, I do not hear them on the RC7620. DTMF reception is blocked.
If I dial out using the same SIM but on 2G then DTMF reception is OK.
Do DTMF tones work over 4G/VoLTE? Is it SIM/network dependent? If DTMF is unreliable over 4G/VoLTE then how do automated phone systems cope?
Thanks for that. Very useful and it works for me. I didn’t realise that AT+WDMM and the +WDDI existed as they are not listed in the latest revision of the RC76xx AT Command Reference pdf. Also the bitmask that you use is shown as “Reserved” in the pdf file too.