dtmf ic

Does these dtmf ics kt 3170 & mt 8870 can decode key press events while hearing ring-back tone (RBT) in on-hook state before accepting call. If no, does any other dtmf ics can do this?

That depends on the exchange. I think on the newer exchanges the ring-back tone is generated locally, I have read that it won't mirror the ring tone that the person on the other end hears.

As for whether the exchange lets you send any audio during the ringing event (before they pick up) that depends on the exchange too. I think at one point it used to work because there were bugging devices sold that you could activate with DTMF during the ringing event.

You probably have to test it on the exchange in question, if it is an old exchange then it would have more chance of working.