My voice echoing on calls - earpiece AND headphones. iPhone 4s

[Wingsurfer]

Hey folks,
When making a call from my iphone 4s I often use a pair of standard headphones for the audio & speak into the bottom of my phone. This is exactly the same way I used my 3gs but when using the 4s in this way I can hear my own voice coming back through the headphones. I have also noticed that when using the phone as 'normal' up to my ear I can hear my own voice coming out of the earpiece.
Any one else noticed this?

 

[screenwotcher]

Hi I sometimes get an echo when recieving calls quite offputting I have iphone4 but i used to get it on my old nokia n95 thought it was something with the network at the time thought someone would have come up with an answer.
cheers john