Relating to this sentence in the article: > I've never heard of a call center system that can accept touch tones seamlessly while a call is active, and it woul

Relating to this sentence in the article: > I've never heard of a call center system that can accept touch tones seamlessly while a call is active, and it would take extremely sophisticated audio processing capabilities to be able to do that, since the frequencies used by touch tone keys heavily overlap the frequencies of human speech. It's actually happening all the time. VoIP systems _do_ extract touch tone (DTMF) from the call and convert them to appropriate out-of-band messages (either on RTP or SIP, there are multiple standards). This might also happen with VoLTE, although I didn't verify it myself. So, while the request was indeed weird, there's nothing technically strange about typing touch tones at any point in a call. Regarding the fact that those frequencies overlap with human speech, it's expected because they were designed to be transferred over phone lines, which are made for human speech frequencies. Since landlines here in Switzerland have been converted to VoIP several years ago, I often hear DTMF tones appearing from nowhere in the middle of a call and covering the voice of the other person. The reason is easy: some intermediate system detected a tone and sent the corresponding SIP/RTP message, while also filtering the tone out of the audio. On the other end of he line, that out-of-band message triggered the generation of an actual in-band tone, whence the result.