If I am in a call and someone is trying to call me, my phone does not bleep to let me know that another caller is trying to reach me - I cannot see how to set this up in the settings. Nor does it show any 'missed call' notifications. It is only if the person leaves me a voicemail, that I know they've tried to reach me.
The option you're referring to is called call waiting to turn it on open your dialer press the 3 dots tap settings and then supplementary services then toggle call waiting on please note not all carriers support this service
