what is the meaning of beep in during calling?

[mokbon]

Hello

I want to know the meaning of "beep in" while someone's calling

When A hang the phone, he said B beep in

I think this is kind of interruption during calling

Give me some details please

 

[birdeen's call]

When you're talking on the phone and you have a call waiting feature on, you hear a beep when there's another person calling you.

 

[Barb_D]

Our conference calling system announces that someone has joined the conference call with a beep.

I agree that the call waiting feature is the more likely situation, but it's possible that someone else "beeped in" to mean joined the call.