Disable Sidetone?

I was talking on an iPhone today and notice that my own voice is fed back to myself (a function called sidetone?). Not my cup of tea I have to say, is there a way to disable it?

Also, I can make/ receive call and hear the other person clearly, but the other end can't hear me at all even though I made sure that "mute" is not on. Anyone knows how to solve this, or is this an operator issue?

Thanks!