I've seen a couple of posts about the Samsung Galaxy s4 having a bit of a problem with echo: Sometimes just on the listener's side, other times both people can hear the echo...
Anyway, if you want to solve your echo problem on your Samsung, then one tool that might help is noise supression
This solution doesn't really solve why the echo is happening on your s4, but it's an easy way to filter out background noises such as echo.
How to turn on noise suppression for a Samsung s4
- On the phone, click the menu button, then navigate in settings and scroll down until 'Noise Suppression' shows up.
- Tick the box to check mark it and the echo should be gone.
- Noise suppression also helps with complaints about muffled sound