http://www.open-source-soft.narod.ru/dtmf_cs.7z C# DTMF detector and generator classes. It was used completely fixed point arithmetic, so algorithms as fast as possibly.
Good sourse, all work.
Poor implementation that will only detect the "tones" that were generated by this library. For better code comments, check the similar C++ project associated with the author of this one.
Bad...project. Don't know why the developer wasted time to write this.