[kelnos]

That app doesn't allow you to inject the tones into an in-progress call; it just plays the tone. If the phone is in speakerphone mode it might work, though would probably still be unreliable. If not, then it just won't work.

[ajb]

Yeah, the echo canceller is going to try to make that not work, and DTMF tones are simple enough that it will likely succeed.