When you’re on a call and a new call comes in, the new call is sent to voicemail. If you want to be notified of new calls instead, turn on call waiting.
To turn call waiting on:


Do one of the following:
Tap Additional settings, then turn Call waiting on 
When call waiting is on, if you're on a call and a new call comes in, you can answer it. The first call is put on hold. Tap 
To turn call waiting off, go to Additional settings, then turn Call waiting off 