Your iPhone is incredibly smart. It can do all kinds of wonderful tasks simultaneously. For example, you probably already know that it will alert you if you have a call coming in while you are already on another call. Your iPhone springs into action and displays the person’s name or number, as well as three options: Decline Incoming Call, Answer & Hold Current Call, and Answer & End Current Call.
This is part of the call waiting feature on your iPhone, and it’s great if you’re expecting an important call or if you want to add the caller to a conference call that you’ve set up.
However, the rest of the time you might just find it annoying and intrusive (and anyone you put on hold or hang up on to take the new call probably finds it rude and insulting). In that case, you can turn off call waiting by following these steps:
On the Home screen, tap Settings.
The Settings app appears.
Tap Phone.
The Phone screen appears.
Tap Call Waiting.
The Call Waiting screen appears.
Tap the Call Waiting switch to Off.
Your iPhone disables call waiting.