Echo of the outgoing audio is jamming the DTMF tone. It is normal to silence any outgoing audio after the first digit.
Note that the UK had to change its dial tone when it introduced DTMF, as the original dialtone was rich in harmonics and particularly effective at jamming DTMF.
[quote=“david55”]Echo of the outgoing audio is jamming the DTMF tone. It is normal to silence any outgoing audio after the first digit.
Note that the UK had to change its dial tone when it introduced DTMF, as the original dialtone was rich in harmonics and particularly effective at jamming DTMF.[/quote]