Apple's advanced smartphones has a few bugs in the system. Some users complained that the battery drained faster when in a particular time zone. Then according to several threads on Apple's forums on the internet, hundreds of iPhone users 4S experience audio echo when making a voice call using the headset cable.
"When using Apple's hands-free headset to make calls, I get the echo problem," wrote one iPhone owner on Apple forums 4S. "This is not imminent, can vary from 30 seconds to 9 minutes after the call begins, before finally starting the annoying echo that. If I unplug the headset, its echoes will reverberate disappear but will return when I plug the headset back" he complained.
IPhone 4S predecessor, the iPhone 4 also have defects in the system. A bug in the software prevents the alarm function of the handset to work. Initial production IPhone 4 also has reception problems. Funnily enough, this problem only appears when he grasped a certain way. But the second problem has been fixed. So just wait for the iPhone 4S repair schedule.