I'm probably not the best person to comment but I can say that I have noticed echo (and some strange noise artifacts) when using a SPA-3000 connected to the FXS port of a provider-supplied SPA-2000. In that hookup I had to play with gain levels to get the echo down to an acceptable (barely audible) level. In testing what is essentially the same type of setup here, I don't notice any of that. Since there's a world of difference between that and a copper pair from a telephone company, all I will say is that it sounds better to me with that particular hookup, and let it go at that.