Ihe iPhone 4/4s echo effect is something I started to notice after the update to iOS 6 but only if I insert the cable after I picked up or made a call on the iPhone.
There's no echo at all if the cable is securely inserted before any call activity (call/receive) takes place.
I think this is the echo effect Westone is referring to and I can't believe it has anything to do with the EPIC MICS Cable.
Just an idea....
But it would explain why some people experience the effect and others don't