Sure you can get reliable DTMF detection on 70%-80% of call paths with
no echo cancellation,

Fair enough. You say "sure you can get reliable DTMF detection on 70%-80% of call paths with no echo cancellation". OK, you forgot to mention that this is achievable with text-book algorithms and that exist advanced algorithms with reliability close to 100%. From my point of view , no need further arguing this issue and this thread for me is closed.

With respect

koliqi